CHAPTER 7 MATH Flashcards
Significant figures
Using more digitales than necessary to calculate and report the results of lab determination has several disadvantages:
1.Only use the digits necessary for precision of determination.
2. Using more suggest more accuracy than is the case.
3. Possibility of overlooking a decimal and making an error judging the magnitude of answer.
4. Digits in a number needed to express the precision of measurement: significant figures.
How many digital are significant?
Use the known accuracy of the method to determine the number of digits significant in the answer - retain 1 more figuren than this:
1.Bun is reported AS 11.2 mg/dL- this would mean that result is accurate between 11.15 to 11.25 - result should be reported as 11q mg/dL ( accuracy of most bun produces is +/ - 10%)
In addition / subtraction:
206.1 206.1
7.56 7.8
0.8764. 0.9
- In multiplication / division:
32.973 / 4.3 = 7.7 ( figures in final product/ quotient should not exceed the smallest number of significant figures of any one factor.
Rounding off number
Test results sometimes produce insignificant digits.
Necessary to round off number so result does not imply accuracy or precision greater than the test is capable of delivering. You want to indicate a value without over standing confident.
General rules:
1. last digital one to be retained is < 5, digits should left unchanged
2. last digit on to be retained is >5, the last digit is increased by 1.
3. Digits is 5, the to the last digit reported is changed to the nearest even number :
Example:
3.19 3.2
3.12 3.1
3.15 3.2
3.25 3.2
3.35 3.4
Working with significant figures
3 rules of significant figures and zeroes
- Numbers that contain zeroes at the end of the number.
When a number contain a zero or zeroes part of that number, the zeros are considered to be significant to that number and are never dropped out of the number. - Number that contain zeroes at the end of the number.
When a number greater than 1 contains a zeros at the end of the number or to the3 right of the decimal place, the zero or zeroes are considered to be significant. - Numbers less than 1 that contain zeroes to the right of the decimal point.
When a number is less than 1, any zero that is between the decimal point and the first nonzero number within the number is Not considered to be significant.
Exponents
Exponents are used to indicated that numbers must be multiply by itself as many times as indicated by the exponent.
The number to be multiplied is calles the base.
The exponent is written as a small superscript figure to the immediate right of the base figure and can be called the power of the base.
Expressions of solution concentration (w/v)(V/V)(%)
Weight (mass) per unit volume (W/V)
Volume per unit volume (v/v)
Percent (%)
Solutons are made up of a mixture of substances.
1.2 main parts
2.The solute: the substance that is being dissolved
3. The solvent: the substance into which the solute is being dissolved
EXPRESSION OF SOLUTION CONCENTRATION (W/V) (V/V) ( %)
1.WEIGHT (MASS) PER UNIT VOLUME (W/V)
USED M OST OFTEN WHEN A SOLID CHEMICAL IS MDILUTED IN A LIQUID.
A STANDARD SOLUTION IS USUALLY EXPRESSED AS MG/ML.
2.Volume per unit volume (v/v)
Liquid chemical is diluted with another liquid.
3. Percent
Usually means grams or milliliters of solute per 100 ml of solution
What is of this is this?
What units of measurement are used?
Solute + solvent(water) = solution
Proportions and ratios
proportions are used to determine a quanity from a given ratio.
A ratio is an amount of something compared to an amount of something else.
Ex: a formula calls for 5g of NaCl in 1000mL of solution. If only 500 mL of solution is needed, how much Nacl is requied?
Conertration of solutions V1 x C1 = V2 x C2
The volume of one solution (V1) time the concentration of that solution (C1) equals the volume of the second solution (V2) times the concentration of the second solution (C23) .
V1xcC1= V2 x C2. Or V1C1 = V2C2
Dilutions (DILUTIONS OF SPECIMENS)
It i often necessary to make dilutions of specimens being analyzed or to make weaker solutions from stronger solutio.
1. A dilution is an expression of concentration and refers to the volume or number of parts of the substance to be diluted in the total volume, or part, of the final solution.
Diluting specimens
Dilution factor
single dilutions = calculation of the concentration of a single dilution use of dilution factors.
Dilution
1.Standard solutions
2. BLANK SOLUTIONS
standard solution
1. A standard solution is one that contains a known, exact amount of the substance being measured.
2. Working standards.
3. These are prepared from the stock solution.
4. Standards used in spectrophotometry.
Blank solutions
1. A blank solution contains reagent used in the procedure, but it does not contain the substance to be measured.
Chapter 4 ]
Simple dilutions
a 1 to 4 dilution of serum is to be made.
The total volumes of the dilution is to be 100 uL
What volumes of serum and difluente ( deionized water) are needed?
Solve this problem, use ratio and proportion.
1 part sample volume = x parts sample volume
——————————. ————————————
4 part total volume. 100 parts total volume
Cross multiplying the equation yields the follwing:
(1) x ( 100 ) = (4) x (x)
100 = 4x
100/4 = x
25 = x
25.0 uL is the sample (serum) volume.
100.0 - 25.0, or 75.0 uL, is the diluyente volume.
DILUTION VARIATIONS
EXAMPLE:
If you had a dilution in which you needed 0.5 parts sample to 9.5 part diluyente, what is the value of the actual dilution you performed?
To solve this dilution problem :
Because 0.5 is < 1, 0.5 must be multiplied by 2.
0.5x 2 = 1.0
The denominator value of 10.0 ( 0.5 sample volume + 9.5 diluyente volume ) is also mutliplied by 2.
0.5 + 9.5 = 10
10 x 2 = 20
The value woukld be a 1 to 20 dilution.
