Key Calculations quiz

1. 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

17g

0.34g

Question 1 of 17

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

Depends on the temperature of the surroundings

Depends on the reagents

Exothermic

Endothermic

Question 2 of 17

3. What is the meaning of the word mole in Chemistry?

Moles are the units for amount of substance. 1 mole of a substance is its relative formula mass in grams (e.g. 1 mole of magnesium is 24 g)

A mole is a small burrowing mammal

Moles are the units for amount of substance. (1 mole is 10 g of a substance)

Moles are the units for amount of substance. 1 mole of an element is its atomic number in grams (e.g. 1 mole of magnesium is 12 g)

Question 3 of 17

4. Use Q=mcΔT and c=4.18J/°C/g. A spatula of sodium fluoride is put into a boiling tube with 25cm³ of water. The temperature drops from 22.0°C to 18.6°C. What is the total heat energy change?

355 J

1944 J

355 kJ/mol

1944 kJ

Question 4 of 17

5. 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 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.

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.

Question 5 of 17

6. To determine the formula of a metal oxide by combustion, magnesium is heated in a crucible. Why is the crucible is cooled, weighed, reheated, cooled, re-weighed, and so on?

To ensure all the magnesium oxide to escape

To allow any water to escape

To make sure the mass is still going down so the magnesium is still reacting

To make sure a constant mass has been reached and there is no more magnesium left to react

Question 6 of 17

7. Calculate the relative formula mass(Mr) of ethanol (C₂H₅OH)

25

46

41

45

Question 7 of 17

8. In a combustion calorimetry experiment, 0.78g of ethanol (C₂H₅OH) produced 12,540 J of heat energy. Calculate the molar enthalpy change.

-738 kJ/mol (Amount = 0.78/46 = 0.017 mol. Answer = 12540/1000/0.017 = 738 kJ/mol)

-425 kJ/mol (Amount = 23/0.78 = 29.5 mol. Answer = 12540/29.5 = 425 kJ/mol)

-213 kJ/mol (Amount = 46/0.78 = 59.0 mol. Answer = 12540/59.0 = 213 kJ/mol)

-369 kJ/mol (Amount = 0.78/23 = 0.034 mol. Answer = 12540/1000/0.034 = 369 kJ/mol)

Question 8 of 17

9. Complete the following expression: mass =

amount (in moles) / Mᵣ

amount (in moles) x Mᵣ

Aᵣ / Mᵣ

Mᵣ / amount (in moles)

Question 9 of 17

10. What mass of calcium bromide will fully react with 71g of chlorine?

480 g

120 g

200g

240 g

Question 10 of 17

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

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 dm³ or 24,000 cm³)

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

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

Question 11 of 17

12. 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 N₂O₅. Molecular formula is N₄O₁₀

Empirical formula is N₄O₁₀. Molecular formula is N₂O₅

Empirical formula is N₂O₅. Molecular formula is also N₂O₅

Empirical formula is NO₂.₅ Molecular formula is N₂O₅

Question 12 of 17

13. What is meant by the term empirical formula?

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

Baby food for emperors

A method of calculating the ratios of masses in an equation

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

Question 13 of 17

14. A beaker of 2 dm³ of ammonium nitrate solution contains 1 mol of ammonium nitrate. What is the concentration of the solution?

0.5 mol/dm³

0.5 dm³/mol

0.0005 mol/dm³

2 mol/dm³

Question 14 of 17

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

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

(12+13)/2 = 12.5

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

(12x13)/100 = 1.56

Question 15 of 17

16. Work out the empirical formula of an oxide of chlorine contains 7.1 g of chlorine and 1.6 g of oxygen.

Cl₄O

Cl₄O₂

Cl₂O₂

Cl₂O

Question 16 of 17

17. State the expression for calculating % yield.

% yield = (actual amount of products/theoretical amount of products)

% yield = (theroretical amount of products/actual amount of products)

% yield = (actual amount of products/theoretical amount of products) x 100

% yield = (theroretical amount of products/actual amount of products) x 100

Question 17 of 17

Key Calculations quiz

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