Chemistry Chapter: Moles and Stoichiometry

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Questions and Answers

What is the correct formula to determine the moles of a solution?

Moles of Solution = Volume of Solution / Conc.of Solution

Moles of Solution = Conc.of Solution + Volume of Solution

Moles of Solution = Conc.of Solution * Volume of Solution (correct)

Moles of Solution + Volume of Solution = Conc.of Solution

Which of the following is true about an empirical formula?

It shows the exact number of atoms in a compound.

It provides the relative molecular mass of the compound.

It is always the same as the molecular formula.

It represents the simplest whole-number ratio of atoms in a compound. (correct)

What is the correct relative molecular mass for the empirical formula CH2, if n is 3?

42 (correct)

In the context of stoichiometry, what is the main focus during calculations?

Mole ratios Signup and view all the answers

If water reacts with calcium oxide, what is the product formed?

Calcium Hydroxide Signup and view all the answers

Given 28 tonnes of calcium oxide, what is the number of moles calculated?

500,000 moles Signup and view all the answers

What is the mass of calcium hydroxide produced from 28 tonnes of calcium oxide?

37 tonnes Signup and view all the answers

Which reactants are typically present in excess in chemical reactions?

Excess reactants Signup and view all the answers

What is the correct percentage purity of a copper sample if the mass of CuO calculated is 0.8g from an initial sample of 5.0g?

84% Signup and view all the answers

What is the theoretical maximum mass of CuSO4 produced from 0.2 mol of CuO?

32g Signup and view all the answers

If the actual mass of CuSO4 obtained is 28g, what is the percentage yield?

87.5% Signup and view all the answers

Which property is NOT characteristic of acids?

Turns litmus paper blue Signup and view all the answers

Which reaction correctly illustrates the reaction of an acid with a metal carbonate?

HNO3 + Na2CO3 -> NaNO3 + H2O + CO2 Signup and view all the answers

What is the pH value of an acidic solution?

Below 7 Signup and view all the answers

What happens when solid acid salts are dissolved in organic solvents?

They remain as simple molecules Signup and view all the answers

What is the role of H+ ions in acidic solutions?

To conduct electricity Signup and view all the answers

What defines a salt in chemistry?

An ionic compound that consists of a cation and an anion. Signup and view all the answers

What is the primary factor in determining the method of preparing a salt?

The solubility of the salt and reagents in water. Signup and view all the answers

Which of the following methods is used to prepare an insoluble salt?

Precipitation of two soluble solutions. Signup and view all the answers

During the precipitation process, what is the first step?

Identify and mix the solutions. Signup and view all the answers

What type of salts does the method involving acid and excess solid typically produce?

Soluble salts that do not contain Group 1 or ammonium ions. Signup and view all the answers

In the process of preparing soluble salts, what must the solids reacting with acids be?

In excess and insoluble. Signup and view all the answers

What by-product can result from the reaction of an acid with an insoluble carbonate?

Water and carbon dioxide. Signup and view all the answers

What is the standard method for obtaining a residue after performing a precipitation reaction?

Filter the mixture through a filter paper. Signup and view all the answers

What is the oxidation state of oxygen in peroxides?

-1 Signup and view all the answers

Which element typically has an oxidation state of +1 when bonded with metals?

1 Signup and view all the answers

In the reaction of respiration, what happens to carbon in glucose?

4 Signup and view all the answers

Which of the following best describes a non-redox reaction?

600 Signup and view all the answers

What oxidation state do transition metals typically exhibit?

0 Signup and view all the answers

In the Haber process, what is the oxidation state change for nitrogen?

-3 Signup and view all the answers

What is the oxidation state of hydrogen in hydrochloric acid (HCl)?

1 Signup and view all the answers

What is the sign of ΔH for an endothermic reaction?

ΔH > 0 Signup and view all the answers

Which of the following statements describes bond breaking in chemical reactions?

Energy is absorbed from the surroundings. Signup and view all the answers

What trend occurs in metallic properties across a period in the periodic table?

Metallic properties decrease. Signup and view all the answers

Which of the following correctly states the relationship between groups and valence electrons?

Valence electrons are determined by the group number minus ten for Groups 13 to 18. Signup and view all the answers

What happens to the size of an atom as you move down a group in the periodic table?

The size of the atom increases. Signup and view all the answers

In an endothermic reaction, how does the energy of the reactants compare to the energy of the products?

Energy of reactants < Energy of products Signup and view all the answers

What trend is observed in metallic properties as you move down a group in the periodic table?

Metallic properties increase. Signup and view all the answers

How is bond energy defined?

The energy absorbed or released to break or form one mole of a chemical bond. Signup and view all the answers

Study Notes

Moles of Solution

Moles of solution calculated using the formula: Moles = Concentration × Volume.
Concentration units: mol/dm³ or g/dm³; Volume unit: dm³.

Empirical & Molecular Formula

Empirical Formula: Simplest ratio of atoms of each element in a compound.
Example: Copper oxide with 8g Cu and 1g O.
Molecular Formula: Actual number of atoms of each element in a molecule.
Relative Molecular Mass (Mr) calculated as: n × Relative Mass of Empirical Formula.
Example: For propene (CH₂) with Mr 42, n calculated as 3.

Stoichiometry

Emphasis on mole ratios; answers should be in decimals with appropriate significant figures.
Example of stoichiometry problem with CaO and water leading to Ca(OH)₂, calculating maximum mass using mole ratio.
Mass conversions: 1 tonne = 1000 kg; 28 tonnes = 28,000 kg = 28,000,000 g.
Balanced equation required for accurate calculations.

Limiting & Excess Reactants

Many reactions use excess amounts of one reactant.
Example of copper purity calculation based on mass of CuO present; % purity found to be 84%.

Percentage Yield

Theoretical yield is mass calculated from reaction equations; actual yield is obtained from experiments.
Actual mass is often lower than theoretical due to issues like incomplete reactions or losses during the process.
Example calculation of percentage yield based on 28g of CuSO₄ from 0.2 mol of CuO, resulting in a yield of 87.5%.

Acids & Bases

Acids: Produce H⁺ ions in water, sour taste, conduct electricity, pH < 7, and turn blue litmus red.
React with metals, bases, and carbonates:
- Acid + Reactive Metal → Salt + Hydrogen.
- Acid + Base → Salt + Water.
- Acid + Metal Carbonate → Salt + Water + CO₂.
Solid acid salts release H⁺ ions in water but behave differently in organic solvents.

Salts

Ionic compounds made of cations and anions formed by replacing H⁺ ions in acids.
Preparation methods vary based on solubility of salt and reagents:
- Precipitation for insoluble salts.
- Acid + Excess Solid for soluble salts containing Group 1/Ammonium.
- Titration for other soluble salts.

Precipitation Method

Mix two soluble solutions to form an insoluble salt.
Standard procedure: Determine solutions, mix, filter, rinse, and dry precipitate.

Acid + Excess Solid Method

For soluble salts not containing Group 1/Ammonium ions.
Solid must be in excess to ensure complete utilization of acid.

Oxidation States

Group 1 metals: +1 oxidation state.
Group 2 metals: +2 oxidation state.
Specific non-metals have defined states: Fluorine (-1), Hydrogen (+1 or -1), Oxygen usually (-2).
Transition metals and lanthanides typically have positive oxidation states.

Identifying Reactions

Redox Reactions involve oxidation and reduction (e.g., respiration, photosynthesis, and the Haber process).
Non-redox reactions, such as acid-base reactions (neutralization), show no change in oxidation states.

Endothermic and Exothermic Reactions

Endothermic: Energy absorbed, temperature decreases, ∆H > 0.
Exothermic: Energy released, temperature increases, ∆H < 0.

Bond Energy:

Amount of energy related to breaking or forming chemical bonds.
Energy change calculated as: ∆H = Total Energy absorbed - Total Energy released.

Periodic Table Overview

Elements arranged by increasing atomic number in periods (horizontal) and groups (vertical).
Groups share similar valence electrons and chemical properties.
Across a period: decrease in metallic properties, increase in non-metallic properties.
Down a group: increase in metallic properties, decrease in non-metallic properties.

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Description

Test your knowledge on calculating moles of a solution, determining empirical and molecular formulas, and understanding stoichiometry. This quiz also covers limiting and excess reactants, providing fundamental concepts essential for mastering chemical reactions. Prepare to apply these concepts to solve real-world chemical problems.