Chemistry Midterm Syllabus Class 7th PDF

# Midterm Marathon for Class 7th Chemistry ## By Ananaya Ma'am ## Today's Goals - Acids, Bases and Salts - Physical and Chemical Changes - Water Waste Story - Water: A Precious Resource ## Chapter No. 01 ### Acids, Bases and Salts ### Acids and Bases - A diagram shows orange juice, lemon, yogu...

# Midterm Marathon for Class 7th Chemistry ## By Ananaya Ma'am ## Today's Goals - Acids, Bases and Salts - Physical and Chemical Changes - Water Waste Story - Water: A Precious Resource ## Chapter No. 01 ### Acids, Bases and Salts ### Acids and Bases - A diagram shows orange juice, lemon, yogurt, tamarind, and baking soda. - Items with sour taste contain acids - Items with bitter taste contain bases (alkalies) ### Acids - These substances taste sour because they contain acids. - The chemical nature of such substances is acidic. - The word acid comes from the Latin word *acere* which means sour. - The acids in these substances are natural acids. - A diagram shows a bottle of vinegar. - The acids prepared from the minerals of the earth are called mineral acids. Mineral acids are man-made acids. - A diagram shows bottles of hydrochloric acid, sulphuric acid, and nitric acid. - Natural acids are weak acids. - Mineral acids are strong acids. - Examples of weak acids: citric acid, acetic acid - These acids are edible. #### Strong Acids and Weak Acids - Strong acids are very dangerous to drink. Even the dilute solutions of strong acids are extremely harmful to drink. - Carbonic acid is used in fizzy soft drinks and water. - A diagram shows hands touching a can, with a fizzing reaction taking place. #### Which of the following is a weak mineral acid? - a) H₂SO₄ - sulphuric acid - b) HCl - hydrochloric acid - c) HNO₃ - nitric acid - d) H₂CO₃ - carbonic acid #### Diluting Acids - A diagram shows the correct way to dilute acid: adding acid to a beaker containing water. - A diagram shows the incorrect way to dilute acid: adding water to a beaker containing acid. - **Imp:** Always add acid to water and *not* water to acid. ### Properties of Acids - The important properties of acids are given below: - Acids have a sour taste. - Acids turn blue litmus to red. - Acids conduct electricity (They are electrolytes). - A diagram shows litmus paper changing from blue to red. - When an acid is in water, we get a solution of electricity. That is, acid solutions allow electric current to pass through. - **Imp:** Electrolytes: solutions that conduct electricity. #### Antacids - If someone is suffering from the problem of acidity after overeating, we can take baking soda remedy. - This is because baking soda is sodium hydrogencarbonate which reacts with excess hydrochloric acid in the stomach and neutralizes it. - *NaHCO₃* - This gives relief to the person suffering from acidity. - A diagram shows a stomach experiencing heartburn, and a person who feels better after taking an antacid. #### Which of the following will neutralize acidity in the Stomach? - a) citric acid - b) lemon - c) baking soda - d) both a and b ### Bases - **Bitter - कड़वे** - Bases are those chemical substances which have a bitter taste. - Bases are the chemical opposites of acids. - A base is a chemical substance which can neutralize an acid. - **Gequalize / सम** - A diagram shows several different bases and their uses: Sodium Hydroxide soaps, Sodium Carbonate Detergents, Sodium Fluoride Toothpaste, Calcium Hydroxide Cement, Ammonia Fertilizers, Bases used in Labs. #### Bases are _ in taste and _ to touch. - a) soapy & bitter - b) soapy & sour - c) bitter & soapy - d) none #### Water Soluble Bases: Alkalis - Bases which dissolves in water without any chemical reaction have a special name. They are called alkalis. - Some of the common water-soluble bases (or alkalis) are: Sodium hydroxide (NaOH), Potassium hydroxide (KOH), Calcium hydroxide, Ammonium hydroxide. - **All alkalis are bases but all bases are not alkaloids.** - A diagram shows a beaker containing NaOH, and the breakdown of the molecules into Na⁺ and OH^-. - **Na₂OH** (Sodium hydroxide) is soluble in water. ### Properties of Bases - The important properties of water soluble bases (or alkalis) are given below : - Bases have a bitter taste - **कडवे** - Bases feel soapy to touch - **G slippery** - A diagram shows a person washing their hands with soap, and a person feeling with their hands. - **B-Base** - **→Bitter** - **→ Blue colour in Litmus.** - **A diagram shows a beaker containing dil. NaOH with an iron nail, a battery, a light bulb lit, and litmus paper changing from red to blue.** - Bases turn red Litmus to blue. - Bases conduct electricity. ### Uses of Bases - **Mg(OH)₂** - Magnesium hydroxide is used as an antacid to neutralize excess acid in the stomach and cure indigestion. - Sodium hydrogen carbonate is used as baking soda in cooking food, for making baking powders, as an antacid to cure indigestion and in soda-acid fire extinguishers. - A diagram shows a bottle of magnesium hydroxide, a box of baking soda, and a fire extinguisher. #### Acid Properties #### Base Properties #### Indicators - An indicator is a 'dye' that changes colours when it is put into an acid or a base. An indicator gives different colours in acid and base. - **Plichen= fungi + algae** - A diagram shows lichens (fungi and algae) as an indicator. - Red - Litmus paper - Blue ### Indicators - An acid turns blue litmus to red. - A base (for alkali) turns red litmus to blue. - **Natural - Jurmeric** - **→Litmus paper.** - Litmus is a natural indicator (Whose neutral colours is purple). When an acid or base is added to it. But methyl orange and phenolphthalein are synthetic indicators. - The neutral colours of methyl orange is 'orange'. - A diagram shows strips of litmus paper changing color. #### Natural - Litmus paper - Jurmeric - China rose #### Synthetic - Phenolphthalein - Methyl orange #### Phenolphthalein - A diagram shows a bottle of phenolphthalein and two beakers. The beaker with a base solution is pink, and the beaker without is colorless. #### Red Cabbage Extract - A diagram shows a beaker of red cabbage extract in three different solutions: - Acid: red - Extract: purple - Alkali: yellow #### Methyl Orange - A diagram shows a bottle of methyl orange and two beakers. The beaker with an acidic solution is red, and the beaker with a basic solution is yellow. ### Strength of Acid & Base - Neutral substances have a pH of exactly 7. Pure water is a neutral substance (it is neither acidic nor basic). So, the pH of pure water is 7. - **neutralisation γχη** - **Acid + Base** - **↓** - **Salt + Water (H₂0)** #### Acid Strength - **Acid strong & base weak** - **↓** - **Salt + water** - **Salt** - **acidic** - A diagram shows a pH scale and two people, one holding a "1" (acid) and the other holding a "4" (base). #### Strength of Bases - **7 → 14** - **Strong base** - **Dark blue** - **or Violet** - A diagram shows two people, one holding a "10" and the other holding a "14". ### Salts - **acid + base → salt + water** - **Strong Strong Neutral** - Then we will get a salt NaCl; This is called sodium chloride. - 'Salt' is a general name and it does not refer only to sodium chloride. - **HCl + NaOH → NaCl + H₂0** - **Neutral Salt.** - A diagram shows a reaction between HCl and NaOH producing water and NaCl, and another diagram shows a pile of salt. #### Types of Salt - **Neutral salt** → neutral - **SA + SB → Salt + water** - **Acidic** - **SA + WB → Salt + water** - **Basic** - **WA + SB → Salt + water** - **S - strong** - **W - weak** - **A - acid** - **B - base** - A diagram shows a pile of salt. ### Self Defense by Animals and Plants Through Chemical Warfare - A wasp stings a human. - A honeybee stings a human. - A wasp stings a human. - **Acid/Base** - **Aard** (ants) - **→ Baking soda** - **Acid and base react.** ### Plants and Animals are Sensitive to pH Changes - (i) **Soil pH and Plant Growth** - Most of the plants grow best when the pH of the soil is close to 7. If the soil is too acidic or too basic (too alkaline), the plants grow badly or do not grow at all. The soil may be acidic or basic naturally. - ***ACIDIC SOIL*** - A diagram shows a person pouring water into soil, and a diagram showing acidic soil. - **Base** - **neutral** ### pH in digestive system - A photo shows a person experiencing stomach pain, and a bottle of antacid. ### Acid Bases and Salt - **Salt** - formed by reaction of acid with base. - **Indicator** - 2 types - **1. Natural** - litmus paper, turmeric - **2. Synthetic** - phenolphthalein, methyl orange - **Acids - sour in taste** - **Turn blue litmus red** - **Conduct electricity in solution** - **Bases - soapy to touch** - **Bitter in taste** - **Turn red litmus blue** - A diagram shows the relationship between acids, bases, and salts. ## Chapter No. 02 ### Physical and Chemical Changes ### Physical and Chemical changes - Broadly, these changes are of two kinds, physical and chemical. - **physical chemical** ### Physical Changes - **Solid, liquid, gas** - Properties such as shape, size, colour and state of a substance are called its physical properties. - A change in which a substance undergoes a change in its physical properties is called a physical change. - A physical change is generally reversible. - In such a change, no new substance is formed. ### Topic: Physical and Chemical Changes #### Which of the following is a physical change? - A) Rusting of iron. - B) Combustion of magnesium ribbon - C) Burning of a candle. - D) Melting of wax - **A diagram shows a candle burning and the reaction:** - **CO₂H₂O vapour** ### Chemical Change - **Rusting of iron** - **Iron + atmosphere** - **↓** - **जग लग गया** (Rusting) - **Rust** - **Chemical Change** - A diagram shows an iron chain with rust starting to develop. ### Chemical Change - Get a small piece of a thin strip or ribbon of magnesium. Clean its tip with sandpaper. Bring the tip near a candle flame. It burns with a brilliant white light. - **Magnesium (Mg) + Oxygen (O₂) → Magnesium oxide (MgO)** - **chemical 2Mg + O₂ → 2MgO Change** - **A diagram shows a piece of burning magnesium, and the reaction written out.** ### Chemical Change - **Mg + O₂ → 2MgO** - **X** - **chemical change** - A diagram shows a burning candle. ### Chemical Change - On dissolving the ash in water it forms a new substance. This change can be written in the form of the following equation: - **Magnesium oxide (MgO) + Water (H₂O) → Magnesium hydroxide [Mg(OH)₂]** - **MgO + H₂O → Mg(OH)₂** - **Base** - **Chemical Change** ### Chemical Change - **vinegar + baking soda** - **↓** - **CO₂ gas - new product** - **chemical charge** - A diagram shows a container of vinegar and baking soda reacting, creating bubbles in the mixture. ### Topic: Physical and Chemical Changes #### Which of the following is/are true when milk changes into curd? - (1) The state is changed from liquid to semi-solid (correct). - (ii) It changes color (incorrect). - (iii) It changes taste (correct). - (iv) The change cannot be reversed (correct). #### Choose the correct option from below: - a) (i) and (ii) are correct - b) (ii) and (iii) are correct - c) (i), (iii) and (iv) are correct - d) (i) to (iv) are correct ### Chemical Change - New product & chemical - **Carbon dioxide (CO₂) + Lime water [Ca(OH)₂] → Calcium Carbonate (CaCO₃) + Water (H₂O)** - When carbon dioxide is passed through lime water, calcium carbonate is formed, which makes lime water milky. The turning of lime water into milky is a standard test of carbon dioxide. - A diagram shows clear lime water and a beaker with milky water after CO₂ is added. - **lime water Ca(OH)₂ CO₂ milky colour** ### Chemical Change - **Copper - ताँबा - meddish brown** - **Copper sulphate + Iron → Iron sulphate + Copper** - **↓** - **blue green reddish** - **Copper Sulphate** - **→ Iron Sulphate** - A diagram shows a beaker with blue copper sulphate solution; iron nails added to the solution, turning the solution green and causing a reddish deposit on the nails. ### Topic: Physical and Chemical Changes #### #Q. A student took a solution of copper sulphate in a beaker and put a clean iron nail into it, leaving it for about an hour. - A) What changes do you expect? - **Blue-green solution कील & iron nail - red coating** - B) Are these changes chemical in nature? (correct) - C) Write a word equation for the chemical change, if any. - **CuSO₄ + Fe → FeSO₄ + Cu** ### Chemical Change - **Heat, light, or any other radiation (ultraviolet, for example) may be given off or absorbed.** - **Sound may be produced.** - **A change in smell may take place or a new smell may be given off.** - **A colour change may take place.** - **A gas may be formed.** ### Prevent Rusting of Iron - **Zinc, chromium** - This process of depositing a layer of zinc on iron is called galvanisation. The iron pipes we use in our homes to carry water are galvanised to prevent rusting. - **Iron + oxygen & water vapour** - **↓** - **Iron oxide Rust** - **A diagram shows the process of electrogalvanizing.** ### Topic: Physical and Chemical Changes #### Which of the following is a chemical change? - A) Twinkling of stars - B) Cooking of vegetables - C) Solidifying water - D) Boiling of water ### Topic: Physical and Chemical Changes #### #Q. If you leave a piece of iron in the open for a few days, it acquires a film of brownish substance, called rust. - A) Do you think rust is different from iron? **Yes.** - B) Can you change rust back into iron by some simple method? **No.** - C) Do you think formation of rust from iron is a chemical change? **Yes.** - D) Give two other examples of a similar type of change. - **① cooking of food** - **② _ _ _ ** - **Front Oxygen & moisture water vapour (Iron oxide) Rust** ### Physical changes - Any change to the physical properties of a substance is called a physical change. - Physical changes are usually reversible as no new substance is formed. - It is the same substance but with changed physical properties. ### Chemical changes - 1. A change in which one or more new substances are formed is called a chemical change. - 2. Usually, a chemical change involves a chemical reaction, which forms new products. - **Example: Rusting of Iron or burning wood.** ### Physical and Chemical changes ### Rusting - When substances made of Iron are exposed to oxygen and moisture in the atmosphere, it forms a red layer, which is called rust. - The formation of rust can be represented by the following reaction: - **4Fe + 3O₂ → 2Fe₂O₃. The chemical formula for rust is Fe₂O₃.nH₂O. More the moisture in the air, the quicker the formation of rust.** ## Chapter No. 03 ### Waste Water Story - **5min** ### What is Sewage? - Sewage is wastewater released by homes, industries, hospitals, offices, and other users. It also includes rainwater that has run down the street during a storm or heavy rain. The water that washes off roads and rooftops carries harmful substances with it. Sewage is a liquid waste. Most of it is water, which has dissolved and suspended impurities. - **Sewage - liquid** - **↓** - **Solid waste, liquid, gases.** ### QUESTION #### Sewage is mainly a _? - a) liquid waste (correct) - b) solid waste. - c) gaseous waste. - d) mixture of solid and gas. ### QUESTION #### Which of the following is wastewater? - a) Water trickling from a damaged tap. - b) Water coming out of a shower. - c) Water flowing in a river. - d) Water coming out of a laundry. (correct) ### Wastewater Treatment Plant (WWTP) - **5M** - Treatment of wastewater involves physical, chemical, and biological processes, which remove physical, chemical, and biological matter that contaminates the wastewater. - Wastewater is passed through bar screens. Large objects like rags, sticks, cans, plastic packets, napkins are removed. - A diagram shows wastewater being filtered through a series of bars. ### Wastewater Treatment Plant (WWTP) - Water then goes to a grit and sand removal tank: The speed of the incoming wastewater is decreased to allow sand, grit, and pebbles to settle down. - A diagram shows a sluice gate controlling the flow of water ### Wastewater Treatment Plant (WWTP) - The water is then allowed to settle in a large tank which is sloped towards the middle. Solids like feces settle at the bottom and are removed with a scraper. - This is the sludge. - A skimmer removes floatable solids, like oil and grease. - Now water so cleared is called clarified water. - A diagram shows a large tank with a sludge scraper, with a skimmer on top. - **Did waste \ Skimmer \ Water \ ->Sludge** ### Work in absence of O₂ - The sludge is transferred to a separate tank where it is decomposed by the anaerobic bacteria. The biogas produced in the process can be used as fuel or can be used to produce electricity. - **Electricity Biogas Anaerobic bacteria Sludge.** - **A diagram shows the anaerobic process.** ### Wastewater Treatment Plant (WWTP) - Air is pumped into the clarified water to help aerobic bacteria to grow. Bacteria consume human waste, food waste, soaps, and other unwanted matter still remaining in clarified water. - **2 work in the presence of O₂** - A diagram shows a tank of clarified water with air being pumped in. ### Aerobic bacteria - After several hours, the suspended microbes settle at the bottom of the tank as activated sludge. - The water is then removed from the top. - The activated sludge is about 97% water. The water is removed by sand drying beds or machines. Dried sludge is used as manure, returning organic matter and nutrients to the soil. - **chlorine - lakes** ### QUESTION #### The system of a network of pipes used for taking away wastewater from homes or public buildings to the treatment plant is known as __? - a) sewers - b) sewerage (correct) - c) transport system - d) treatment plant ### QUESTION #### Which of the following is *not* a source of wastewater? - ya ra hai - a) Sewers - b) Homes - c) Industries - d) Hospitals (correct) ### QUESTION #### Given below is a jumbled sequence of the processes involved in a wastewater treatment plant. Arrange them in their correct sequence. **(HW)** - a) Sludge is scraped out and skimmer removes the floating grease. - b) Water is made to settle in a large tank with a slope in the middle. - c) Large objects like plastic bags are removed by passing wastewater through bar screens. (correct) - d) Sand, grit, and pebbles are made to settle by decreasing the speed of the incoming wastewater. - e) Wastewater enters a grit and sand removal tank. ## Chapter No. 04 ### Water: A Precious Resource ### World Water Day - You are perhaps aware that 22 March is celebrated as the world water day! - A photo shows a water droplet splashing into a body of water. ### How Much Water is available? - **Salt water** - **Saline 87%** - **All Water on Earth** - **Freshwater 3%** - A diagram shows a pie chart representing all the water on earth; the majority is saltwater, and only 3% is freshwater. - **Use** - **Icecaps and Glaciers 68.7%** - **Surface water 0.3%** - **Lakes 87%** - **Rivers 2%** - **Swamps 11%** - **Ice** - **K Phad** ## Water Cycle - A diagram shows the water cycle: the sun evaporating water, clouds forming, precipitation, and water moving into lakes. - **Condensation** - **Clouds** - **Evaporation** - **Lake** - **Lakes** - **Water cycle** ### Groundwater: An Important Source of Water - The level of this layer is called the water table. The water table varies from place to place. - The process of seeping of water into the ground is called infiltration. The groundwater thus gets recharged by this process. At places, the groundwater is stored between layers of hard rock below the water table. - A diagram shows the process of rain infiltrating into the ground, and the water table. - **Rain** - **Groundwater** - **Hand pump** - **Stream or lake** - **Recharge** - **Water table** - **Aquifer** - **Groundwater** ### Depletion of Water Table - **Increasing population** - **G leads to depletion of water due to more consumption & more usage in daily activities.** - A photo shows a growing population. ### Depletion of Water Table - **Increasing industries** - Water is used by industries. Almost everything that we use needs water somewhere in its production process. The number of industries is increasing continuously. Water used by most of the industries is drawn from the ground. - **Agricultural activities** - A majority of farmers in India depend upon rains for irrigating their crops. - **Watering crops at reguler intervals** ### Water Management - The rainwater can be used to recharge the groundwater. This is water harvesting or referred to as rainwater harvesting. - **Drop by drop** - **Drip irrigation:** Drip irrigation is a technique of watering plants by making use of narrow tubing's which deliver water directly at the base of the plant. - A diagram shows drip irrigation. ### QUESTION #### You have been asked to maintain a garden. How will you minimize the use of water? - **① drip irrigation (drop by drop)** - **② Required amount of water added** - **③ water harvesting system in the garden** ### QUESTION #### Which one of the following is *not* responsible for water shortage? - a) Rapid growth of industries - b) Increasing population - c) **Heavy rainfall** (correct) - d) Misanagement of water resources. ### QUESTION #### Choose the correct option. The total water _ ? - a) in the lakes and rivers of the world remains constant. - b) under the ground remains constant. - c) in the seas and of the world remains constant. - d) of the world remains constant (correct) - A diagram shows a pie chart of saltwater (97%) and freshwater (3%), and the water cycle. - **3% fresh water** - **97% salt water** - **Water cycle** - **Lake** - **evaporate** - **condensation** - **Rain** - **Clouds** - **precipitation** ### Water cycle - Water is a colourless liquid, which constitutes the major part of the Earth for survival. 71% of the Earth consists of water, hence the Earth is also called a blue planet. - **Waste (a precious resource)** - A diagram shows two pie charts explaining freshwater and saltwater, as well as a section explaining water management. ### Freshwater and Saltwater - Freshwater is the pure and naturally occurring water on the Earth's surface in rivers, lakes and underground as groundwater. - Saltwater is also called saline water, which consists of some amounts of dissolved salts in it. Saltwater is present in oceans and seas. ### Water Management - **Rainwater harvesting or water harvesting:** The process of collecting rainwater, which recharges the groundwater, is called as rainwater harvesting. - **Drip irrigation:** Drip irrigation is the process of watering the crops directly to the roots of the plants using narrow pipes. - **Bawris:** A traditional way of rainwater storage and recharge. - **a) Yes \ b) No** - **Thank You Baccho** - A photo shows a cartoon character of a teacher giving a presentation with a yellow school bus theme.