Question

Using the molarity equation, calculate how many grams of salt you need in order to make 80ml of a 2M solution (MW = 58.44g/mole)?

Answer 1

9.35g

Step-by-step explanation:

The molarity equation establishes that:

`\textrm{molarity}=\frac{\textrm{moles  of solute}}{\textrm{liters of solution}}`

So, we have information about molarity (2M) and volume (80 ml=0.08 l), with that, we can find the moles of solute:

`\textrm{moles of solute}=\textrm{molarity}*\textrm{liters of solution}`

`\textrm{moles of solute}= 0.08 \textrm{ l} *2\textrm{ M} = 0.16 \textrm{ mol}`

The mathematical equation that establishes the relationship between molar weight, mass and moles is:

`\textrm{molar weight}= \frac{\textrm{mass}}{\textrm{moles}}`

`\textrm{MW}= \frac{\textrm{m}}{\textrm{n}}`

We have MW (58.44g/mole) and n (0.16 mol), and we need to find m (grams of salt needed) to solve the problem:

`\textrm{m} = \textrm{MW * n}= 58.44\frac{\textrm{g}}{\textrm{mol}} * 0.16 \textrm{ mol} = 9.35 \textrm{ g}`