Group 2 metal carbonates thermally decompose to produce a metal oxide and a gas - AQA - GCSE Chemistry Combined Science - Question 6 - 2018 - Paper 1

Given the relative formula mass (Mₕ) of the Group 2 carbonate is 197:

We know that the formula mass includes the contributions from the carbon and oxygen atoms:

• Total mass from C and O:
  • C: 1 × 12 = 12
  • O: 3 × 16 = 48

Total from C and O = 12 + 48 = 60.

Now, to find the relative atomic mass (Aₕ) of the Group 2 metal (M):

M + 60 = 197

M = 197 - 60 = 137.

Thus, the relative atomic mass (Aₕ) of the Group 2 metal is 137.

The Group 2 metal with a relative atomic mass of 137 is barium (Ba).

To calculate the gradient (m) from the graph, we can use the formula:

$m = \frac{\Delta y}{\Delta x}$

From the graph, take points (0.5 g, 100 cm³) and (2.0 g, 300 cm³):

• Change in Y (Gas volume): 300 - 100 = 200 cm³
• Change in X (Mass): 2.0 - 0.5 = 1.5 g

Hence, the gradient is:

$m = \frac{200}{1.5} = 133.33$

Thus, the gradient is approximately 133.33 and the unit is cm³/g.

From the graph, if 24 dm³ is equivalent to 24000 cm³, and using the previously calculated gradient of approximately 133.33:

First, identify mass from the gradient: If 240 cm³ corresponds to 1.8 g based on previous readings, setup the ratio:

Using the direct proportion:

$\frac{24000}{(2.0 g)} = \frac{24000}{x}$

So, we have:

Calculating: $\text{Mass} (x) = 24000 \times \frac{2.0}{240} = 200 g$

Using the gradient determined: From the earlier equation, Total molecular volume correlates with gas produced, thus:

Relative formula mass (Mₕ) can be expressed from the ratio of gas volume: That leads to:

Mₕ = mass (200 g) or directly incorporate prior values, yielding: Resulting mass is estimated around 145 g.