Key Calculations quiz

1. Use Q=mcΔT and c=4.18J/°C/g. A strip of magnesium is added to a beaker with 200cm³ of copper (II) sulfate. The temperature starts at 21.7°C and rises to a maximum of 23.1°C. What is the total heat energy change?

1247 J

1944 kJ

2.153 kJ

1170 J

Question 1 of 17

2. State the units of molar enthalpy change.

J/⁰C/mol

kJ/⁰C

kJ/mol

mol/⁰C

Question 2 of 17

3. Describe how to carry out an acid-alkali titration

1) Pipette 25cm³ of alkali into a conical flask. 2) Add indicator. 3) Fill a burette with acid, record the initial volume. 4) Whilst swirling the flask, add the acid dropwise until the indicator changes colour. 5) Record the volume and calculate the volume of acid which was added. 6) Repeat until two concordant results (within 0.2cm³ of each other). 7) Result is the average of all concordant results.

1) Pipette 25cm³ of alkali into a conical flask. 2) Add indicator. 3) Fill a burette with acid, record the initial volume. 4) Whilst swirling the flask, add the acid dropwise until the indicator is just about to change colour. 5) Record the volume and calculate the volume of acid which was added. 6) Repeat until two concordant results (within 0.2cm³ of each other). 7) Result is the average of all concordant results.

1) Pipette 25cm³ of alkali into a conical flask. 2) Add indicator. 3) Fill a burette with acid, record the initial volume. 4) Whilst swirling the flask, add the acid dropwise until the indicator changes colour. 5) Record the volume and calculate the volume of acid which was added. 6) Repeat until three concordant results (within 0.2cm³ of each other). 7) Result is the average of all concordant results.

1) Pipette 25cm³ of alkali into a conical flask. 2) Add indicator. 3) Fill a burette with acid, record the initial volume. 4) Whilst swirling the flask, add the acid dropwise until the indicator is just about to change colour. 5) Record the volume and calculate the volume of acid which was added. 6) Repeat until three concordant results (within 0.2cm³ of each other). 7) Result is the average of all concordant results.

Question 3 of 17

4. What mass of carbon dioxide is produced when 24g of carbon undergoes completely combustion?

176 g

88g

44 g

24 g

Question 4 of 17

5. 200 cm³ of potassium sulfate solution has a concentration of 2 mol/dm³. What amount of potassium sulfate does it contain?

50 mol

0.4 mol

0.01 mol

400 mol

Question 5 of 17

6. What are the units for amount in Chemistry?

Moles

mol/dm³

Grams

g per 100g of solvent

Question 6 of 17

7. In the thermal decomposition of calcium carbonate, we might expect 50g of calcium carbonate to produce 28g of calcium oxide. If instead only 24g of calcium oxide is produced, what is the percentage yield?

0.56 %

85.7 %

56 %

0.857 %

Question 7 of 17

8. A sample of carbon contained 98.90% carbon-12 and 1.10% carbon-13. Calculate the relative atomic mass of carbon

(12x13)/100 = 1.56

((12x98.90)+(13x1.10))/100 = 12.01

((13x98.90)+(12x1.10))/100 = 12.99

(12+13)/2 = 12.5

Question 8 of 17

9. Calculate the relative formula mass(Mr) of zinc phosphide (Zn₃P₂)

120

272

223

257

Question 9 of 17

10. What is the empirical formula of a compound in which 0.48 g of carbon combines with 0.08 g of hydrogen and 0.64 g of oxygen?

C₂H₄O₂

CH₄O

CH₂O

C₄H₂O

Question 10 of 17

11. Complete the following expression: mass =

Aᵣ / Mᵣ

amount (in moles) / Mᵣ

Mᵣ / amount (in moles)

amount (in moles) x Mᵣ

Question 11 of 17

12. What is the meaning of the term Molar Volume?

The volume of 1 mole of gas at 100 ⁰C (24 dm³ or 24,000 cm³)

The volume of 1 mole of gas at r.t.p (24 cm³ or 24,000 dm³)

The volume of 1 mole of gas at r.t.p (24 dm³ or 24,000 cm³)

The volume of 1 mole of gas at 100 ⁰C (24 cm³ or 24,000 dm³)

Question 12 of 17

13. A graph shows the solubility of sodium chloride in water at 50°C is 34g/100g. At that temperature, what mass of sodium chloride will dissolve in 200g water?

0.68g

68g

0.34g

17g

Question 13 of 17

14. In a chemical reaction, the overall molar enthalpy is -87 kJ/mol. Is this reaction exothermic or endothermic?

Exothermic

Depends on the temperature of the surroundings

Depends on the reagents

Endothermic

Question 14 of 17

15. What is meant by the term empirical formula?

A method of calculating the ratios of masses in an equation

Baby food for emperors

A chemical formula that shows the actual numbers of the different types of atoms in a molecule

A chemical formula that shows the simplest ratio of the numbers of atoms in a compound

Question 15 of 17

16. An oxide of nitrogen contains 26% nitrogen and 74% oxygen and has a relative molecular mass of 108. Find the empirical and molecular formulae for the oxide.

Empirical formula is N₄O₁₀. Molecular formula is N₂O₅

Empirical formula is N₂O₅. Molecular formula is also N₂O₅

Empirical formula is N₂O₅. Molecular formula is N₄O₁₀

Empirical formula is NO₂.₅ Molecular formula is N₂O₅

Question 16 of 17

17. To determine the formula of a metal oxide by combustion, magnesium is heated in a crucible. Why is a lid lifted from time to time?

To allow some magnesium oxide smoke to escape

To allow carbon dioxide to escape

To stop the crucible heating up too much

To allow oxygen in so the magnesium fully reacts

Question 17 of 17

Key Calculations quiz

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