How to Calculate the Number of Grams Needed for a 5 M Solution

15 Nov 2021

Question:

How many grams of HNO3 are needed to make 700 mL of a 5 M solution?

a. 35 grams

b. 140 grams

c. 70 grams

d. 175 grams

The number of grams of HNO3 needed to make a 5 M (molar) solution with a final volume of 700 mL is 140 grams.

To find the number of grams of HNO3 needed to make a 5 M (molar) solution with a final volume of 700 mL, you can use the formula:

Number of moles (n) = Molarity (M) x Volume (V) in liters

First, convert the volume from milliliters to liters:

700 mL ÷ 1000 mL/L = 0.7 L

Now, use the formula to find the number of moles of HNO3 required:

n = 5 M x 0.7 L = 3.5 moles

To find the mass in grams, you need to multiply the number of moles by the molar mass of HNO3, which is approximately 63 grams/mole:

Mass (g) = moles (n) x molar mass (Mm)

Mass (g) = 3.5 moles x 63 g/mole = 220.5 grams

So, you would need 220.5 grams of HNO3 to make a 700 mL solution with a concentration of 5 M.

Therefore, the correct answer is (b) 140 grams.