Chemistry Skills: Study Guide*

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Chemistry Skills: Study Guide for S1

Identify the following terms:

Which of the following is a set of controlled observations that tests a hypothesis?

Experiment

A theory is a(n)

Explanation supported by many experiments

A hypothesis is a(n)

Tentative explanation of observation

A control is a

standard for comparison

A constant is a factor that

is not allowed to change during an experiment

At the end of an experiment, the scientist forms a conclusion based on the

data obtained

Scientific Notation:

- It is used to make very large or very small numbers easier to handle.

For example, the number 45,000,000 can be written as --> 4.5 x 10^-7 power. The "7" tells you that there are seven decimal places between the right side of the four and the end of the number.

Another example: 2.641 x 10^6. The "6" tells you how many decimal places between the right side of the 2 and at the end of the number --> 2,641,000.

Very small numbers are written with negative exponents. For example, 0.0000378 can be expressed as 3.78 x 10^-5. The "-5" tells you that there are 5 decimal places between the right side of 3 and the end of the number. It translates to moving to the left.

Key Factors: Big numbers move to the right.

Small numbers move to the left.

When you multiply two numbers in scientific notation, you must add their exponents. Here is a following examples:

(4.5 x 10^12) x (3.2 x 10^36) = (4.5)(3.2) x 10^{12 + 36} = 14.4 x 10^44 --> 1.44 x 10^45.

Steps into understanding the problem:

1) You isolate the first numbers in both of the problems. --> (4.5)(3.2)

2) Multiply it by 10 and make sure to add both of the exponents --> "10 ^ 12 + 36"

3) With the result of; "14.4 x 10^44" it is a good idea to check where your decimal falls into the category of "14.4", it is not between the numbers "1 & 10"

4) When moving your decimal to the left, you have to increase the number of the exponent depending on how much. It changes the exponent to "45"

5) Your final answer shall include "14.4 x 10^45"

When you divide two numbers, you must subtract denominator's exponent from the numerator's exponent.

2.8 x 10^14 2.8

____________ = __________ x 10 {14-7} = 0.875 x 10^7 = 8.75 x 10^6

3. 2 x 10^7 3.2

5.7 x 10^19 5.7

_____________ = ___________ x 10 {19 - (-9)} = 1. 84 x 10^19+9 = 1.84 x 10^28

3.1 x 10^-9 3.1

Steps into understanding this problem:

1) You isolate the first numbers in both of the problems. --> 5.7 / 3.1 = 1.84 or 2.8 / 3.2 = .875

2) Make sure to subtract both of the exponents

3) Check the decimal places on the whole numbers & decimal numbers

4) If it doesn't follow the rule, then make it possible to follow the rule, such as ".875 --> 8.75"

5) There are expectation to the rule, = "1.84"

6) With the exponents, you must subtract one exponent. Your results should end up with one less exponent on either of the whole # rules.

7) 1.84 x 10^28 or 8.75 x 10^6

Adding and Subtracting using scientific notation

Whenever you add or subtract two numbers in scientific notation, you must makes sure they have the same same exponents. Your answer will then have the same exponent as the numbers you add or subtract. Here are some examples.

4.2 x 10^6 + 3.1 x 10^5 --> make exponents the same, either a 5 or a 6. --> 42 x 10^5 + 3.1 x 10^5 = 45.1 x 10^5 = 4.51 x 10^6

Steps:

1) The decimal place matters what place you move it toward too. It depends on what number you chose. Always move it to the right.

2) 45.1 x 10^5 = 4.51 x 10^6 , the reason it is a "6" is because the rule of the number being a whole number does not satisfy. In order to move it to the left you have to increase the exponent. In order to move it to the right you have to decrease the exponent.

*The same rule and steps apply to subtracting*

Significant Figures

There are three very important rules when it comes into determining significant figures.

1) Zeros at the beginning of a number are never significant.

2) Zeros at the end of the number are not significant unless

3) Zeros that are between two non zero numbers are always significant

Therefore, the number 21,500 has three significant figures: only three of the digits are important - the two, the one, and the five. The number 10,210 has four significant figures because only the zero at the end is not considered significant. All of the digits in the number 10,005 are significant because the zeros are in between two non zero numbers.

There is one exception to the second rule. Consider the following measured values:

It is 1200 miles from my town to atlanta

It is 1200.0 miles to my town to atlanta

"The quantity 1200.0 miles" is more precise than "1200 miles". The decimal point in the quantity "1200.0 miles" means that it was measured very precisely.

Rule #2: Zeros at the end of the number are not significant unless there is a decimal point in the number. A decimal point anywhere in the number makes zeros at the end of the number significant.

0.00000007290 --> The beggining numbers of zero are not significant. The zero at the end of the number is significant because there is a decimal point in the number.

Rounding Significant Figures

In numerical problems, it is often necessary to round numbers to the appropriate number of significant figures. Each of the following examples contain 4 significant figures.

42,008,000 → 42, 010, 000

12,562,425 → 12,560,000

0.0001798323 → 0.0001799

120→ 120.0

Multiplying and Dividing significant numbers “rounding”

When multiplying and dividing numbers, you need to round your answers to the correct number of significant figures.

Count the number of significant figures in each number

Round your answer to the least significant figures.

Examples:

4560/14 = 325.714285714 *14 has 2 significant figures, you must round it to the least* = 330 (it has 2 sig figs)

13.1 x 1.2039 = 15.77109 *13.1 has 3 sig figs, must round to the least* = 15.8 (it has 3 sig figs)