Question

Q) What is the concentration in moles per litre of:

a) a sodium carbonate solution containing 53 g of the salt (Na2CO3) in 1 litre?

b) a copper(ll) sulfate solution containing 62.5 g of the salt (CuSO4.5H20) in 1 litre?

Answer 1

Answer:

The concentration of a substance in solution, expressed as the number moles of solute per liter of solution.

Answer 2

Answer:

A) 0.5 mol/litre

B) 0.25 mol/litre

Explanation:

A) Concentration = $\frac{Amount (mol)}{Volume}$

Over here we have laid out the equation for concentration. The volume was provided ( 1L ) but the number of moles wasn't, so this is a variable we'll have to figure out before carrying out the equation.

Equation to find the number of moles = $\frac{Mass}{Mr}$

In the question the mass is given (53g), now we'll have to calculate the Mr:

Na2CO3 = (23x2) + 12 + (16x3) = 106 Mr

Now that we have both the Mass and Mr, calculating the number of moles will be pretty straightforward.  $\frac{Mass}{Mr}$ =  $\frac{53}{106}$  put that into your calculator and you'll find the answer to be 0.5.

Since we now have the number of moles, we can easily find the concentration by following the equation for concentration.

$\frac{Amount (mol)}{Volume}$ = $\frac{0.5}{1}$ this will obviously give us 0.5.

The answer including the units would be 0.5 mol/litre.

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B) Here we'll have to do the exact same thing ,the only difference is the number of grams and Mr.

Concentration = $\frac{Amount (mol)}{Volume}$

The volume was provided ( 1L ) but the number of moles wasn't, so, just like part A, we'll have to figure out the number of moles.

Number of moles = $\frac{Mass}{Mr}$

In the question the mass was given but the Mr wasn't. we'll have to calculate it:

Mr for CuSO4 CuSO4 = 64 + 32 + (16x4) = 160

Mr for 5H2O = 5(2+16 ) = 90

160 + 90 = 250

Now that we have the Mr we are able to follow the equation to find the number of moles: $\frac{Mass}{Mr}$ = $\frac{62.5}{250}$ Put that into you calculator and it'd give you 0.25.

Since we have both the number of moles and the volume, we can directly plug our values into the equation for concentration:

$\frac{Amount (mol)}{Volume}$ = $\frac{0.25}{1}$ this would give you an obvious answer of 0.25.

The answer including the units would be 0.25 mol/litre

I hope this helps