Question

Calculate the mass of potassium hydrogen tartrate that is measured to prepare 100 mL of a 0.150 mol/L standard solution

Answer 1

How many moles do you need? That's M x L = ?
Then moles = grams/molar mass. You know molar mass and you know moles, solve for grams KHtartrate

Answer 2

100 mL = 0.1 L

To determine amount of potassium hydrogen tartrate needed in moles:
n KC4H5O6 = (0.1 L) x (0.150 mol/ 1 L) = 0.015 moles

Convert this amount into mass of potassium hydrogen tartrate by using its molar mass, M. The molar mass of potassium hydrogen tartrate is 188.177 g/mol.

m KC4H5O6 = (0.015 moles) x (188.177 g/ 1 mol) = 2.822655 grams

You could combine the two above steps:
m KC4H5O6 = (0.1 L) x (0.150 mol/ 1 L) x (188.177 g/ 1 mol) = 2.822655 grams