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