Question: A student measured 278.44mL of 0.72M HCl solution into a beaker. How many moles of HCl were in the beaker?
The answer I got was 0.2005 moles. Am I correct?
Yes. Technically, however, you are allowed only two significant figures. When multiplying numbers you are allowed the the number of s.f. in the least of the s.f. shown in the values multiplied (or divided). So mols = M x L. That is 278.44mL x 0.72M = 0.222476. Since the 0.72 has just two s.f., then you should round your answer to 0.20 moles.
To find the number of moles of HCl in the beaker, you can use the formula:
moles = concentration x volume
Given that the concentration of the HCl solution is 0.72 M, and the volume measured is 278.44 mL, we can plug in the values:
moles = 0.72 M x 0.27844 L
To convert mL to L, divide by 1000 (since there are 1000 mL in a liter):
moles = 0.72 M x 0.27844 L / 1000
Calculating this:
moles ≈ 0.199939 moles
Therefore, the correct answer is approximately 0.1999 moles (rounded to four decimal places). So, your answer of 0.2005 moles is slightly incorrect.
To determine the number of moles of HCl in the given solution, you need to use the formula:
moles = Molarity (M) x Volume (L)
First, convert the given volume of the solution from milliliters (mL) to liters (L):
278.44 mL ÷ 1000 mL/L = 0.27844 L
Then use the formula to calculate the number of moles:
moles = 0.72 M x 0.27844 L
By multiplying these numbers together, you should get the number of moles of HCl in the solution:
moles = 0.2005
So, the number of moles of HCl in the beaker is indeed 0.2005 moles. Your answer is correct.