# Question #e73b2

##### 2 Answers

You need **79 mL** of the stock solution.

#### Explanation:

The first thing you need to do is figure out exactly how much nitric acid your stock solution contains. To make the calculations easier, you can assume the you have a **1.00-L** sample of the stock solution.

Use the solution's density to determine what the mass of the sample is

You know that this solution is **70.3%** concentration by mass nitric acidm which means that every **100 g** of solution contain **70.3 g** of nitric acid. This means that you have

Use nitric acid's molar mass to see how many moles would that many grams contain

This means that the **1.00-L** sample will have a molarity of

Now all you have to do is perform a simple dilution calculation

Plug your values into the above equation and solve for

Rounded to two sig figs, the number of sig figs you gave for the volume of the target solution, and expressed in mL, the answer will be

You should use 79.45 ml of the stock solution and make it up to a volume of 2.5L

#### Explanation:

You need 2.5L of 0.5M

So:

So the no. moles

Now we need to find how many grams this is. We get this by multiplying by the weight of 1 mole of

So mass required =

We know that the concentrated form is

This means that 100g of this concentrated solution contains 70.30g of

So now we need to work out what volume of concentrated solution will give us the mass we need:

There are:

So:

The density of the solution = 1.41g/ml

density = mass/volume

So volume = mass/density

So the volume required =