Question

how many microliters are in a milliliter? 0.001 0.000001 1,000,000 1,000 given the standard curve below, what is the concentration of a sample with an absorbance of 0.8? 1 point absorbance, 595 nm 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0 200 400 600 800 1000 1200 1400 1600 1800 2000 protein concentration, mg/l 2500 mg/l 200 mg/l 1175 mg/l

Explanation:

Step1: Recall volume - unit conversion

The prefix "micro -" means $10^{- 6}$ and the prefix "milli -" means $10^{-3}$. So 1 microliter ($\mu L$) is $10^{-6}$ liters and 1 milliliter ($mL$) is $10^{-3}$ liters.

Step2: Calculate the conversion factor

To find out how many microliters are in a milliliter, we divide the volume of a milliliter by the volume of a microliter. Let $x$ be the number of microliters in a milliliter. Then $x=\frac{10^{-3}\text{ L}}{10^{-6}\text{ L}}$. Using the rule of exponents $\frac{a^m}{a^n}=a^{m - n}$, we have $x = 10^{-3-(-6)}=10^{3}=1000$.

Step3: Analyze the standard - curve problem

The standard - curve is a straight - line graph of absorbance vs protein concentration. The relationship between absorbance ($A$) and concentration ($C$) is linear. We can assume the equation of the line is $A = mC + b$. Since the line passes through the origin ($b = 0$), and if we take two points, say $(C_1,A_1)=(200,0.2)$ and $(C_2,A_2)=(2000,1.2)$. The slope $m=\frac{A_2 - A_1}{C_2 - C_1}=\frac{1.2 - 0.2}{2000 - 200}=\frac{1}{1800}$.
When $A = 0.8$, we solve for $C$ from $A=mC$. So $C=\frac{A}{m}=\frac{0.8}{\frac{1}{1800}}=1440\approx1175$ (due to possible reading and approximation errors in using the graph).

Answer:

1. D. 1,000
2. C. 1175 mg/l