Pupil sheet · Relative masses

Where does the mass go? — questions

Name ______________________ Date ____________

Try every question before you use a nudge. Write in full sentences where you are asked to explain.

1. calculate

A pupil heats 4.00 g of blue copper(II) sulfate crystals to constant mass, and 2.56 g of white solid is left. Use the same ratio to calculate the mass of white solid left by (a) 1.00 g of crystals and (b) 6.00 g of crystals.

(a) White solid from 1.00 g: ______________ unit ________

(b) White solid from 6.00 g: ______________ unit ________

Nudge (only if you are stuck): How many times bigger or smaller than 4.00 g is each mass?

2. determine / identify

A metal M forms a nitrate with the formula M(NO₃)₂. Its relative formula mass is 148. (A_r: N 14, O 16. Metals: Na 23, Mg 24, Al 27, K 39, Ca 40.) Determine the relative atomic mass of M, and identify the metal.

A_r of M: ______________ unit ________

The metal M

Nudge (only if you are stuck): Which part of the 148 belongs to the two nitrate groups?

3. calculate

In a blast furnace, iron is made from iron(III) oxide: Fe₂O₃ + 3CO → 2Fe + 3CO₂. Calculate the mass of iron that can be made from 320 kg of iron(III) oxide. (A_r: C 12, O 16, Fe 56.)

Iron: ______________ unit ________

Nudge (only if you are stuck): Find the mass of Fe₂O₃ and of 2Fe in the equation first.

4. calculate

Aluminium powder burns in oxygen to make aluminium oxide: 4Al + 3O₂ → 2Al₂O₃. (A_r: O 16, Al 27.) A chemist needs to make 306 g of aluminium oxide. (a) Calculate the mass of aluminium needed. (b) Calculate the mass of oxygen needed.

(a) Aluminium: ______________ unit ________

(b) Oxygen: ______________ unit ________

Nudge (only if you are stuck): What mass of aluminium oxide does the equation make, counting the big number in front of it?

5. describe

In which order should these steps be done to find the mass of a product from the mass of a reactant?

Write the number of each step in order.

Multiply the product's mass by that same number
Write the balanced equation
Work out the Mr of the reactant and of the product
Multiply each Mr by its big number in the equation
Find the number that turns the equation's mass of reactant into the mass you have

Step 1: ______
Step 2: ______
Step 3: ______
Step 4: ______
Step 5: ______

Nudge (only if you are stuck): You need the equation before you can find any ratio.

6. identify

A pupil heats a basin of hydrated zinc sulfate crystals, lets it cool and weighs it. She does this three times. The table shows her readings. Which mass should she record as the final mass of the basin and solid?

Weighing	Mass of basin and contents / g
Before heating	52.10
After heating 1	51.46
After heating 2	51.31
After heating 3	51.31

Circle one answer.

51.46 g, because it is the first reading after heating
51.36 g, because it is the mean of the three heated readings
51.31 g, because the last two readings are the same
52.10 g, because mass is conserved when crystals are heated

Nudge (only if you are stuck): Did the mass change between each pair of readings?

7. calculate / determine

Washing soda crystals are hydrated sodium carbonate, Na₂CO₃·xH₂O, with relative formula mass 286. Heated to constant mass, they lose all their water and leave sodium carbonate, Na₂CO₃. (A_r: H 1, C 12, O 16, Na 23.) (a) Calculate the relative formula mass of Na₂CO₃. (b) Determine x, the number of water molecules in each formula unit. (c) A pupil heats 10.0 g of washing soda to constant mass. Calculate the mass of sodium carbonate left. (d) Calculate the mass of water lost. Give your answers to (c) and (d) to 3 significant figures.

(a) M_r of Na₂CO₃: ______________ unit ________

(b) x: ______________ unit ________

(d) Water lost: ______________ unit ________

Nudge (only if you are stuck): For (b), which part of the 286 is water? For (c) and (d), the masses keep the same ratio as in one formula unit.