a little trouble with these, kindly help please
1) How many grams of vitamin B12 are present in a 100.0 mL blood serum sample with a vitamin B12 concentration of 148 ng/L?
A)1.48 x 10-8 g
B)1.48 x 10-5 g
C)1.48 g
D)1.48 x 10-9 g
2)Sodium fluoride is added to drinking water. A 25-L sample of city water contains 0.018 g NaF. Express this concentration in molarity.
A)0.018 M
B)18 M
C)0.00072 M
D)0.000017 M
3)If 48 L of city water contains 0.030 g sodium fluoride, what is the concentration in parts per thousand?
A)1.4 ppt
B)0.00063 ppt
C)16 ppt
D)0.0025 ppt
4)15.0 g of KCl is dissolved into a solution with a total volume of 250.0 mL. What is the molarity of the solution?
A)0.804 M
B)1.24 M
C)0.200 M
D)3.75 M
5)An egg yolk with the volume of 3.75 mL contains 5.00 µg vitamin D (cholecalcifoerol). What is the concentration of vitamin D in mg/dL? (1 µg = 10-6 g and 1 dL = 10-1 L)
A)0.0188mg/dL
B)0.750 mg/dL
C)0.133 mg/dL
D)1.30 mg/dL
for others facing these problems,
1.A
2.D
3.B
4.A
5.C
1.
148 ng/L = 148E-9 g/L.
Then g/L is 1.48E-9 g/L x #L = ?
2.
mols NaF = grams/molar mass
M = mols/L
3.
You have 0.030 g in 48,000 g and you want to convert that to g in 1000. So
0.030 g x 1000/48000 = ?
4.
mols = grams/molar mass
Then M = mols/L
5.
5 ug x (1 mg/1000 ug) = ? mg
3.75 mL x (1 L/1000 mL) x (10 dL/L) =? dL
Then mg/dL = ?
on 3. my calculator gives me a crzy answer, 6.25e-4 this cant be right, can it
1) To find the grams of vitamin B12 in the 100.0 mL blood serum sample, we need to convert the concentration from ng/L to g/mL.
First, convert the concentration from ng to g by dividing by 10^9 (since there are 10^9 ng in a g).
148 ng/L / 10^9 = 1.48 x 10^-7 g/mL
Next, we convert mL to L by dividing by 1000 (since there are 1000 mL in a L).
100.0 mL / 1000 = 0.1 L
Now, multiply the concentration in g/mL by the volume in L to get the grams of vitamin B12.
1.48 x 10^-7 g/mL * 0.1 L = 1.48 x 10^-8 g
Therefore, the answer is A) 1.48 x 10^-8 g.
2) To express the concentration of NaF in molarity, we need to calculate the number of moles of NaF in the 25 L sample.
First, convert the mass of NaF from grams to moles using its molar mass. The molar mass of NaF is 22.99 g/mol + 19.00 g/mol = 41.99 g/mol.
0.018 g / 41.99 g/mol = 4.29 x 10^-4 mol
Next, divide the moles of NaF by the volume in liters to get the molarity.
4.29 x 10^-4 mol / 25 L = 1.716 x 10^-5 M
Therefore, the answer is A) 0.018 M.
3) To find the concentration in parts per thousand (ppt), we need to calculate the mass of sodium fluoride in the 48 L of city water.
Convert the mass of sodium fluoride from grams to milligrams.
0.030 g * 1000 mg/g = 30 mg
Next, divide the mass of sodium fluoride by the volume of water in liters and multiply by 1000 to get the concentration in ppt.
30 mg / 48 L * 1000 = 625 ppt
Therefore, the answer is D) 0.0025 ppt.
4) To find the molarity of the solution, we need to calculate the number of moles of KCl in the 15.0 g sample.
First, convert the mass of KCl from grams to moles using its molar mass. The molar mass of KCl is 39.10 g/mol + 35.45 g/mol = 74.55 g/mol.
15.0 g / 74.55 g/mol = 0.201 mol
Next, divide the moles of KCl by the volume in liters to get the molarity.
0.201 mol / 0.250 L = 0.804 M
Therefore, the answer is A) 0.804 M.
5) To find the concentration of vitamin D in mg/dL, we need to convert the volume of the egg yolk from mL to dL and the mass of vitamin D from µg to mg.
Convert the volume of the egg yolk from mL to dL.
3.75 mL / 10 dL/mL = 0.375 dL
Convert the mass of vitamin D from µg to mg.
5.00 µg / 10^3 mg/µg = 0.005 mg
Next, divide the mass of vitamin D by the volume of the egg yolk to get the concentration in mg/dL.
0.005 mg / 0.375 dL = 0.0133 mg/dL
Therefore, the answer is C) 0.133 mg/dL.