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Homework. Chapter 0 - 0, 1, 2, 4 Chapter 1 – 15, 16, 19, 20, 29, 31, 34. Question: . What is the molarity of a 10\% (w/v) solution of glucose?. Parts per million (PPM). PPM.

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homework
Homework
  • Chapter 0 - 0, 1, 2, 4
  • Chapter 1 – 15, 16, 19, 20, 29, 31, 34
question
Question:

What is the molarity of a 10% (w/v) solution of glucose?

slide4
PPM
  • Parts per million is a convenient way to express dilute concentrations. Historically, 1 mg per liter or per 1000 ml is referred to as 1 ppm. However, this is not really the case, as parts per million should be expressed as:

Show that the above equation is equivalent to mg per liter.

slide5
PPM

For dilute solutions, the density of the solution will be the same as water.

Density of solution = Density of water=

1.0 g/ml

question converting ppm to molarity
Question Converting PPM to Molarity

The town of Canton prohibits the dumping of copper solutions that have concentrations greater than 0.3969 ppm. When cleaning the quant lab, Dr. Skeels found a bottle labeled “copper standard - 7 mM”, is it permissible to dump this solution down the drain?

Volunteers??

solution preparation cont d
Solution preparation cont’d

Describe the Preparation of a 500.0 mL of a solution that contains 8.00 mM Cu2+ using CuSO4.5H2O (MW 149.69).

solution preparation cont d1
Solution preparation cont’d

Describe the Preparation of a 500.0 mL of a solution that contains 8.00 mM Cu2+ using CuSO4.5H2O (MW 149.69).

Thus …

slide10
Add ______g CuSO4.5H2O

Into a volumetric flask

Add about _____ ml of water

Swirl to dissolve

And fill to the _____ ml mark

question1
Question
  • Using the 8 mM Cu2+ solution, prepare 20 mL of a 0.25 mM Cu2+ solution.
dilutions
Dilutions
  • To make dilutions of a solution, the following equation should be employed:
question2
Question

Using the 8 mM Cu2+ solution, prepare 20 mL of a 0.25 mM solution.

a more difficult example
A more difficult example
  • Prepare a 500.0 mL of 1 M HCl.
slide16
MW

Wt %

Density

try it out
Try it out …

Consider it in two steps:

(1) Determine concentration of Stock

(2) Make dilution

1 concentration of stock
(1) Concentration of Stock
  • Must find grams of HCl per liter of solution

dHCl=1.19 g/ml

%HCl (w/w)=37%

MW=36.46 g/mol

Mass

HCl per

Liter

Molarity

dilution
Dilution
  • Determined concentration of stock is ______ M HCl. We want a 500.0 mL solution that is 1M.
slide20
NOTE
  • Care must be exercised

when handling strong acids!!

(Always, Always add acid to water)

Add about 300 ml of water first

Then add acid

Dilute to mark

homework1
Homework
  • Chapter 0 - 0, 1, 2, 4
  • Chapter 1 – 15, 16, 19, 20, 29, 31, 34
chapter 3

Chapter 3

Experimental Error

And propagation of uncertainty

suppose
Suppose

You determine the density of some mineral by measuring its mass

  • 4.635 +0.002 g

And then measured its volume

  • 1.13 + 0.05 ml

What is its uncertainty?

significant figures cont d
Significant Figures (cont’d)
  • The last measured digit always has some uncertainty.
3 1 significant figures
3-1 Significant Figures
  • What is meant by significant figures?

Significant figures: minimum number of digits required to express a value in scientific notation without loss of accuracy.

examples
Examples
  • How many sig. figs in:
    • 3.0130 meters
    • 6.8 days
    • 0.00104 pounds
    • 350 miles
    • 9 students
rules
“Rules”
  • All non-zero digits are significant
  • Zeros:
    • Leading Zeros are not significant
    • Captive Zeros are significant
    • Trailing Zeros are significant
  • Exact numbers have no uncertainty

(e.g. counting numbers)

what is the value
What is the “value”?

When reading the scale of any apparatus, try to estimate to the nearest tenth of a division.

3 2 significant figures in arithmetic
3-2Significant Figures in Arithmetic
  • We often need to estimate the uncertainty of a result that has been computed from two or more experimental data, each of which has a known sample uncertainty.

Significant figures can provide a marginally good way to express uncertainty!

3 2 significant figures in arithmetic1
3-2Significant Figures in Arithmetic
  • Summations:
    • When performing addition and subtraction report the answer to the same number of decimal places as the term with the fewestdecimal places

+10.001

+ 5.32

+ 6.130

21.451

21.451

___ decimal places

?

try this one
Try this one

1.632 x 105

4.107 x 103

0.984 x 106

0.1632 x 106

0.004107 x 106

0.984 x 106

+

+

1.151307 x 106

1.151307 x 106

3 2 significant figures in arithmetic2
3-2Significant Figures in Arithmetic
  • Multiplication/Division:
    • When performing multiplication or division report the answer to the same number of sig figs as the least precise term in the operation

16.315 x 0.031 =

?

0.505765

___ sig figs

___ sig figs

____ sig figs

3 2 logarithms and antilogarithms
3-2Logarithms and Antilogarithms

From math class:

log(100) = 2

Or log(102) = 2

But what about significant figures?

3 2 logarithms and antilogarithms1
3-2Logarithms and Antilogarithms

Let’s consider the following:

An operation requires that you take the log of 0.0000339. What is the log of this number?

-4.469800302

log (3.39 x 10-5) =

log (3.39 x 10-5) =

log (3.39 x 10-5) =

Between -5 and -4

____ sig figs

3 2 logarithms and antilogarithms2
3-2Logarithms and Antilogarithms
  • Try the following:

Antilog 4.37 =

2.3442 x 104

23442

___ sigs

rules1
“Rules”
  • Logarithms and antilogs

1. In a logarithm, keep as many digits to the right of the decimal point as there are sig figs in the original number.

2. In an anti-log, keep as many digits are there are digits to the right of the decimal point in the original number.

3 4 types of error
3-4. Types of error
  • Error – difference between your answer and the ‘true’ one. Generally, all errors are of one of three types.
    • Systematic (aka determinate) – problem with the method, all errors are of the same magnitude and direction (affect accuracy)
    • Random – (aka indeterminate) causes data to be scattered more or less symmetrically around a mean value. (affect precision)
    • Gross. – occur only occasionally, and are often large.

Can be detected and eliminated or lessened

Estimated

Treated statistically

absolute and relative uncertainty
Absolute and Relative Uncertainty
  • Absolute uncertainty expresses the margin of uncertainty associated with a measurement.

Consider a calibrated buret which has an uncertainty + 0.02 ml. Then, we say that the absolute uncertainty is + 0.02 ml

absolute and relative uncertainty1
Absolute and Relative Uncertainty
  • Relative uncertainty compares the size of the absolute uncertainty with its associated measurement.

Consider a calibrated buret which has an uncertainty is + 0.02 ml. Find the relative uncertainty is 12.35 + 0.02, we say that the relative uncertainty is

3 5 estimating random error absolute uncertainty
3-5. Estimating Random Error (absolute uncertainty)
  • Consider the summation:

+ 0.50 (+ 0.02)

+4.10 (+ 0.03)

-1.97 (+ 0.05)

Sy = + 0.06

2.63 (+ ?)

3 5 estimating random error
3-5. Estimating Random Error
  • Consider the following operation:

0.010406 =

3 5 estimating random error2
3-5. Estimating Random Error
  • Logarithms antilogs
question3
Question
  • Calculate the absolute standard deviation for a the pH of a solutions whose hydronium ion concentration is

2.00 (+ 0.02) x 10-4

pH = 3.6990 + ?

question4
Question
  • Calculate the absolute value for the hydronium ion concentration for a solution that has a pH of 7.02 (+ 0.02)

[H+] = 0.954992 (+ ?) x 10-7

suppose1
Suppose

You determine the density of some mineral by measuring its mass

  • 4.635 +0.002 g

And then measured its volume

  • 1.13 + 0.05 ml

What is its uncertainty?

the minute paper
The minute paper

Please answer each question in 1 or 2 sentences

  • What was the most useful or meaningful thing you learned during this session?
  • What question(s) remain uppermost in your mind as we end this session?
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