Mass of reactants = mass products. A reactant or a … · 3.Give two examples of a reaction where a...

Chemical measurements – QuestionIT

1. What is the law of conservation of mass?Mass of reactants = mass products.

2. Why might some reactions appear to show a change in mass?A reactant or a product is a gas.

3. Give two examples of a reaction where a change in mass may appear to take place.Metal reacting with oxygen or an acid. Thermal decomposition.

4. Balance the following equations:a) 2H2 + O2 à 2H2Ob) Ca + 2HCl à CaCl2 + H2c) 2Li + 2H2O à 2LiOH + H2d) 4NH3 + 5O2 à 4NO + 6H2Oe) 4K + O2 à 2K2O


1. How many atoms and elements are in the compound sodium aluminate, NaAl(OH)4?Four elements and ten atoms.

2. What do the following formulae tell you?a) 2HClTwo molecules of hydrogen chloride. Each molecule contains one

hydrogen atom and one chlorine atomb) Cl2One molecule of chlorine made of two atoms.

3. An aqueous solution of hydrogen peroxide (H2O2) decomposes to form water and oxygen.a) Write a balanced symbol equation for this reaction. Include

the state symbols.2H2O2 (aq) à 2H2O (l) + O2(g)


b) Why does the water, produced during the reaction, have a lower mass than the original hydrogen peroxide?

Because the oxygen gas produced during the reaction escaped into the atmosphere.

Chemical measurements– QuestionIT

1. What is the relative formula mass of a compound?Sum of the relative atomic masses of the atoms in the numbers shown in the formula.

2. What is the relative formula mass of:a) MgCl2 95b) C6H12O6 180

3. What can be said about the sum of the relative formula masses of the reactants and products of a reaction?In a balanced chemical equation – the sum of the relative formula masses of the reactants in the quantities shown = sum of the relative formula masses of the products in the quantities shown.

Chemical measurements– QuestionIT

4. Why can you have relative atomic masses which are not whole numbers e.g. chlorine is 35.5?Isotopes.

Use of amount of substance (HT) – QuestionIT

1. What is meant by the term ‘mole’? A measure of the chemical amount of a substance.

2. What is the symbol for the unit mole?mol

3. What does ‘Avogadro’s constant’ tell us?Number of atoms, molecules or ions in a mole of a substance.

4. What is the value for Avogadro’s constant?6.02 x 1023 per mol

5. How many atoms in 1 mole of carbon?6.02 x 1023


6. How many atoms in 1 mole of chlorine gas, Cl2?6.02 x 1023

7. What can the following equation tell us about the number of moles of each substance?

Mg + 2HCl à MgCl2 + H2

1 mole of magnesium reacts with 2 moles of hydrochloric acid to form 1 mole of magnesium chloride and 1 mole of hydrogen.

8. What is meant by the term ‘limiting reactant’?A reactant in a reaction which is completely used up when the other reactant is in excess.


9. How many moles of helium atoms are there in 0.04g of helium?0.04/4 = 0.01mol

10. What is the mass of 20 moles of calcium carbonate CaCO3? Answer in kg.40+12+(16x3) = 100100 x 20 = 2,000g = 2kg.

11. Calcium carbonate decomposes to calcium oxide in a kiln in the following reaction: CaCO3 à CaO + CO2Calculate the mass of calcium oxide that can be produced when 300 tonnes of calcium carbonate is heated.Relative formula mass of calcium carbonate = 100 = 100gRelative formula mass of calcium oxide = 56 = 56g 100 tonnes of calcium carbonate makes 56 tonnes of calcium oxideso 300 tonnes make 168 tonnes


12. 0.10g of hydrogen reacts with 3.55g of chlorine to produce 3.65g of hydrogen chloride. Use this information to work out the balancing numbers for hydrogen chloride.

H2 + Cl2 à ___HCl

Mr: H2 = 1 x 2 = 2Mr: Cl2 = 35.5 x 2 = 71Mr: HCl = 1 + 35.5 = 36.5

Then to convert masses to moles use:Moles of H2 = 0.10/2 = 0.05 molMoles of Cl2 = 3.55/71 = 0.05 molMoles of HCl = 3.65/36.5 = 0.1 molDividing the ratio by the smallest number gives 1:1:2 H2 + Cl2 à 2HCl


13. If 4.95 g of ethene (C2H4) are combusted with 3.25 g of oxygen, what is the limiting reactant?

C2H4 + 3O2 à 2CO2 +2H2O

Mr: C2H4 = 28Mr: O2 = 32

4.95/28 = 0.177 mol3.25/32 = 0.102 mol

From the equation: 1 mole of ethene reacts with 3 moles of oxygen. In this case 0.177 mol of ethene will need 0.53 mol of oxygen to react, which we do not have, so oxygen is the limiting factor.

Use of amount of substance – QuestionIT

1. What units can be used for the concentration of a solution?g/dm3

2. What does dm3 mean?1000cm3

3. Give the equation for calculating concentration from the mass of substance and volume of solution.Concentration = mass ÷ volume

4. HT Only: How can you increase the concentration of an aqueous solution?Add more solute and dissolve in the same volume of water; evaporate off some of the water/decrease the volume of water

Use of amount of substance – QuestionIT

5. Calculate the concentration in g/dm3 for 50g of sodium chloride in 2.5dm3 of water.50/2.5 = 20g/dm3

6. Calculate the concentration in g/dm3 of 1.4g of potassium carbonate in 855cm3 of water.(1.4/855) x 1000 = 1.64 g/dm3

7. A teacher has a solution of lithium fluoride with a concentration of 72.6g/dm3. Calculate the mass of lithium fluoride dissolved in 25.0cm3 of solution.25cm3 = 0.025dm3

72.6 x 0.025 = 1.8g

Extracting metals – QuestionIT

1. What is an ore?Metal compound in a rock.

2. What is produced when metals react with oxygen?Metal oxide.

3. What is this process called and why?Oxidation, gain of oxygen.

4. What is reduction in terms of oxygen?Loss of oxygen.

5. What type of ions do metals produce?Positive.

6. Which is more reactive potassium or iron?Potassium.

7. Which two non-metals can be included in the reactivity series?Carbon and hydrogen.


8. Why is gold found as an element in the Earth?Unreactive metal.

9. How are metals, less reactive than carbon, extracted from their ores?Reduction with carbon.

10. HT: Describe oxidation in terms of electrons.OIL – loss of electrons

11. HT: Describe reduction in terms of electrons.RIG – gain of electrons

12. Write the word equation for the reaction between lithium and water.lithium + water → lithium hydroxide + hydrogen


8. Write the balanced symbol equation for the reaction between lithium and water.2Li(s) + 2H2O(l) → 2LiOH(aq) + H2(g)

9. HT: Zinc can be extracted from zinc oxide by heating it with carbon in the blast furnace. Carbon monoxide is also produced. Which reactant is:a) Oxidised? Carbon b) Reduced? Zinc oxide

Reactions of acids – QuestionIT

1. What is produced when acids react with metals?Salt + water.

2. HT: What is a redox reaction?Oxidation and reduction.

3. What is produced when an acid reacts with a carbonate?Salt + water + carbon dioxide.

4. What salt is produced by the following acids?a) Hydrochloric acid Chlorideb) Sulfuric acid Sulfatec) Nitric acid Nitrate

5. How are soluble salts made from acids and insoluble substances?Solid added to acid until no more reacts; excess solid filtered off.

6. Name the process of producing solid salts from salt solution.Crystallisation.


7. Complete the following equations:a) magnesium + sulfuric acid à magnesium sulfate + hydrogenb) sodium hydroxide + hydrochloric acid à sodium chloride + waterc) lithium carbonate + nitric acid à lithium nitrate + water +

carbon dioxide

8. Write a balanced symbol equation, with state symbols, for the reaction between zinc and hydrochloric acid.Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)

9. Higher:Write an ionic equation, with state symbols, to show magnesium reacting with hydrochloric acid.Mg(s) + 2H+(aq) → Mg2+(aq) + H2(g)


1. What ions do aqueous acids contain?H+

2. What ions do aqueous alkalis contain?OH-

3. What is the pH scale?Measure of the acidity or alkalinity of a solution.

4. How can pH be measured?Universal indicator, pH probe.

5. What pH is a neutral solution?7

6. What pH do aqueous acid solutions have?Less than 7.

7. What pH do aqueous alkali solutions have?More than 7.


8. Write a balanced symbol equation for the reaction between hydrogen ions and hydroxide ions.H+(aq) + OH-(aq) à H2O(l)

9. CHEMISTRY ONLY: What are the units for the concentration of a solution?mol/dm3 or g/dm3

10. CHEMSITRY ONLY: What is the concentration of a solution that has 40g of solute in 2dm3 of solution?

Concentration = mass ÷ volume = 40 g ÷ 2 dm3 = 20 g/dm3


11. HT: What is a strong acid?Completely ionised in aqueous solution.

12. HT: Name 3 strong acids.Hydrochloric, nitric, sulfuric.

13. HT: What is a weak acid?Partially ionised in aqueous solution.

14. HT: Name 3 weak acids.Ethanoic, citric, carbonic

15. HT: What is a dilute acid?Contains less solute in the same volume

16. HT: What happens to the hydrogen ion concentration as the pH decreases by 1?Increases by a factor of 10

Electrolysis – QuestionIT

1. Why can a molten or dissolved ionic compound conduct electricity?Free moving ions.

2. What is electrolysis?When an electric current is passed through a molten or aqueous ionic solution and the salt breaks down into simpler substances.

3. What is the name of the electrode that positive ions move to?Cathode.

4. What is the name of the electrode that the negative ions move to?Anode.

5. What is produced at the cathode when lead bromide is electrolysed?Lead.

6. What is produced at the anode when lead bromide is electrolysed?Bromine.


7. What is produced at the cathode is the metal in the solution is more reactive than hydrogen?Hydrogen.

8. What is produced at the anode if the solution does not contain halide ions?Oxygen.

9. HT Only: Write half equations for the reactions that happen at the electrodes during the electrolysis of molten copper chloride.Negative electrode: Cu2+(aq) + 2e− ® Cu(s)Positive electrode: 2Cl−(aq) ® Cl2(g) + 2e−

10. Predict the products of electrolysis of copper sulfate solutionPositive electrode: Oxygen gas; Negative electrode: Copper.

11. HT Only: Write a half equation for the reactions that happen at the electrodes during the electrolysis of copper bromide solution.Negative electrode: Cu2+(aq) + 2e− ® Cu(s)Positive electrode: 2Br−(aq) ® Br2(g) + 2e−


1. Why is electrolysis used to extract aluminium form its ore?Aluminium is more reactive than carbon.

2. Why is electrolysis an expensive way to extract metal from its ore?Large amounts of energy needed.

3. Name the compound from which aluminium is extracted.Aluminium oxide/ bauxite.

4. What is this compound dissolved in before electrolysis?Cryolite.

5. What is the anode made of?Carbon.


6. Describe what happens at the positive electrode during the electrolysis of aluminium oxide.

Oxide ions give up their electrons to form oxygen atoms, these join together in pairs to form oxygen gas, the oxygen reacts with the carbon electrode to make carbon dioxide gas.

6. HT Only: Write half equations for the reactions that occur at the positive and negative electrodes during the production of aluminium.Positive electrode: 2O2−(aq)® O2(g) + 4e−

Negative electrode: Al3+(aq) + 3e− ® Al(l)

Energy Changes part 1 – AnswerIT

1. How would you know if an exothermic reaction had occurred?

The reaction would give out heat/get warmer/ temperature

increase.

2. How would you know if an endothermic reaction had occurred?

The reaction would take in heat/get colder/ temperature decrease.

Energy Changes part 1 – AnswerIT

3. Below is a table of results for four reactions, the temperatures

before and after the reactions are also given.

a/ Which reaction is endothermic? Explain how you know this.

Reaction C, it gets colder/temperature falls.

b/ Which reaction is exothermic? Explain how you know this.

Reaction A, it gets warmer/temperature increases.

Reaction Temperature at start OC Temperature at end OC

A 22 28B 20 20C 21 12D 25 25

Energy Changes part 2 AnswerIT

1. What is meant by the term activation energy?

The minimum amount of energy that particles must have to react.

2. On the reaction profile below what is shown by the letters? A ReactantsB ProductsC Activation energyD Overall energy change/that the reaction is exothermic

Energy Changes part 2 AnswerIT

3. What two things are needed for a chemical reaction to occur?

Reacting particles collide with each other and with sufficient energy.

4. What is an exothermic reaction?Heat energy given out/energy lost to the surroundings

5. What is an endothermic reaction?Heat energy taken in/energy taken in from the surroundings

The energy change of reactions (HT only) AnswerIT1. Which process is exothermic, bond breaking or bond making?

Bond making

2. Explain your answer to question 1

Energy is released/temperature increases

3. How do we calculate the overall energy change of a reaction?

It is the difference between the sum of the energy needed to break bonds in the

reactants and the sum of the energy released when bonds in the products are

formed.

The energy change of reactions (HT only) AnswerIT

4. The bond energy between a hydrogen and a nitrogen atom is 386 kJ/mol, the bond energy between two hydrogen atoms is 432 kJ/mol and the bond energy between two nitrogen atoms is 942kJ/mol. Using these bond energies calculate the overall energy change for the following reaction.

2NH3 à N2 + 3H2

Overall energy change = energy needed to – energy released as break the bonds bonds are made2,316kJ/mol - 2,238kJ/mol

Overall energy change = + 78kJ/mol

5. Is the reaction exothermic or endothermic? Explain your answer.

The reaction is endothermic as the overall energy change is positive.

For the reactantsThere are three nitrogen to

hydrogen bonds in each molecule and there are two

molecules so386kJ/mol x 6 = 2,316kJ/mol

For the productsThere are three hydrogen to hydrogen bonds

(432kJ/mol) and one nitrogen to nitrogen triple bond so

3 x 432kJ/mol + 942kJ/mol= 2,238kJ/mol

Mass of reactants = mass products. A reactant or a … · 3.Give two examples of a reaction where a...

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