Exams Context Grade 7 PDF

Grade 7 1. Introduction 1. What is Chemistry about? Chemistry is the science that deals with the properties, composition, and structure of substances (defined as elements and compounds), the transformations of them, and the energy that is released or absorbed during these processes....

Grade 7 1. Introduction 1. What is Chemistry about? Chemistry is the science that deals with the properties, composition, and structure of substances (defined as elements and compounds), the transformations of them, and the energy that is released or absorbed during these processes. 2. What are the physical properties of matter? The physical properties of matter are: length, color, density, mass, elasticity, pressure, volume, luster. 3. What are the chemical properties of matter? The chemical properties of matter are: toxicity, oxidation states, heat of combustion, chemical stability, flammability, coordination number, reactivity, chemical bonds, enthalpy of formation 2. States of matter 1. Which are the states of matter? The states of matter are solids, liquids, gases and plasma.  2. What are the similarities and di=erences between solids, liquids and gases? Solids Liquids Gases Rigid Not rigid Not rigid Fixed shape Not fixed shape Not fixed shape Fixed mass Fixed mass Fixed mass Fixed volume Fixed volume Not fixed volume Cannot be squashed Cannot be squashed Can be squashed 3. Which are the changes of states of matter? 4. What is “melting point”? Melting point is the temperature where a substance can change from its solid state to a liquid state. 5. What is “freezing point”? Freezing point is the temperature at which a substance undergoes a phase change from a liquid state to a solid state. 6. What is the melting and freezing point of pure water? Pure water has the same temperature of 0oC as both melting and freezing point. 0oC is the temperature at which ice and water coexist. 7. What is “boiling point”? Boiling point is the temperature at which a liquid undergoes a phase change and turns into a vapor. 8. What is the boiling point of pure water? Pure water’s boiling point is 100oC.  9. What are the di=erences between boiling and evaporation? 1. Boiling as a phenomenon occurs at the entire mass of the liquid, while evaporation occurs only on the free surface of the liquid. 2. Evaporation can occur at any temperature, while boiling occurs only in one temperature, which is the characteristic boiling point of a substance. 3. Water 1. What are the basic properties of water? Water is: A fundamental factor in the creation and maintenance of life on our planet. The most common liquid in nature. About 70% of the Earth's surface is covered by water. The main component of living organisms. All animals and plants are made up of up to 95% water. The main component of foods and many materials. 2. Are all bodies consisted of 70% water? No, not all bodies are consisted of 70% water. Infants consist of 80% water, teenagers consist of 70% water and adults consist of around 55-60% water. Animals and pets are consisted of 80% water. 3. What is the chemical symbol of water? H2 O 4. What is the structure of the molecule of water? The molecule of water consists of 2 atoms of hydrogen and 1 atom of oxygen. 5. Why is water is known as an “universal solvent”? Water is known as an “universal solvent” because it can dissolve almost every substance. 6. What is the most abudant form of water on Earth? The most abudant form of water on Earth is saltwater. 7. Describe the water cycle: The water cycle shows the continuous movement of water within the Earth and atmosphere. It is a complex system that includes many di^erent processes. Liquid water evaporates into water vapor, condenses to form clouds, and precipitates back to earth in the form of rain and snow. Water in di^erent phases moves through the atmosphere (transportation). Liquid water flows across land (runo^), into the ground (infiltration and percolation), and through the ground (groundwater). Groundwater moves into plants (plant  uptake) and evaporates from plants into the atmosphere (transpiration). Solid ice and snow can turn directly into gas (sublimation). The opposite can also take place when water vapor becomes solid (deposition). 8. What is the role of the sun in the water cycle? When energy from the Sun reaches the Earth, it warms the atmosphere, land, and ocean and evaporates water. The movement of water from the ocean to the atmosphere to the land and back to the ocean, is fueled by energy from the Sun. 9. What are the uses of water in our everyday life? The uses of water in our everyday life are urban, industrial and agricultural. 4. Mixtures-Solutions 1. Which are the categories in which we divide matter? Matter is divided into pure substances and mixtures. Pure substances are divided into elements and compounds, while mixtures are divided into homogeneous mixtures and heterogeneous mixtures. 2. What is a mixture? Mixture is any system that results from the mixing of two or more substances. 3. What is an heterogeneous mixture? Heterogeneous are the mixtures whose components are distinct with bare eye or a common microscope. 4. What is an homogeneous mixture? Homogeneous are the mixtures whose components are not distinct with bare eye or a common microscope. 5. What are the properties of mixtures? 1. We can mix the components of mixtures in various proportions. 2. The components of a mixture retain many of their properties. 6. What is a solution? Solutions are the homogeneous mixtures, whose components are not distinct with bare eye or a common microscope. 7. What are the parts of a solution? A solution consists of a solvent and a solute. 8. What is a solvent? Solvent is the component of a solution, that has the same physical state as the solution. In liquid solutions the solvent is usually present in a larger proportion. 9. What is a solute? Solute is the component of a solution, that can be solid or liquid and is dissolved from the solvent. In liquid solutions the solute is usually present in a smaller proportion.