Do you know where you come from? because science does

Hi guys,

Imagine a person that went for vacation to a different state from where there home is. During the vacation the person was attack and robbed. He/she was hit in the head, and lost their memory. The person doesn’t remember what happened and has no form of identification. Do you know how to find out where the person might be from?

Recent research indicates that the relative amounts of the isotopes of hydrogen and oxygen in a person’s hair indicate in which part of the United States a person lives. James Ehleringer, a chemist at the University of Utah in Salt Lake City, observes that the concentrations of hydrogen-2 and oxygen -18 in drinking water vary significantly from region to region in the United States. Ehleringer and his colleagues collected hair samples from barbershops in 65 cities and 18 states. Their analyses showed that 86% of the variations in the hydrogen and oxygen isotopes in the hair samples result from the isotopic composition of the local water. Based on their result, the group was able to develop estimates of the isotopic signature of peoples’ hair from various region of the country. Although this method cannot be used to find out the person's physical address, it can give a general region. This method might be helpful for the amnesia person where to look for his/her family.  

Those maps show concentrations of hydrogen-2(top) and    oxygen 18(bottom). Red represents the highest concentration, and blue represents the lowest concentration of each isotope.

Rounding Off Numbers and Significant Figures

Nowadays everyone have a calculator that helps to calculate large numbers, but large numbers are difficult to use in chemical tasks. So, it is very important to know how to round the answer off correctly.

We have two rules for rounding off numbers.

If the digit to be removed

is less than 5 (that is 1,2,3,4), the previous digit stays the same.

For example   2.334 the last digit is 4, which is less than 5, so the previous number 3 will stay the same. The answer is 2.33

           

            is equal to or greater than 5 (that is 5,6,7,8,9), the previous digit is increased by 1.

For example   2.336 the last digit is 6, which is greater than 5, so the previous number 3 will increase by 1. The answer is 2.34

Second part of my post is significant figures.

They are 3 rules that we have to understand to know how to count significant figures.

I.          Leading zeros are never significant.

For example

3 4 5 6 0 0 0 0 0, this number has 4 significant numbers (we don’t

        1   2  3  4                    count the zeros)

II.         Captive zeros are always significant numbers.

For example  

4 6 0 0 2 1, this number has 6 significant numbers

1  2   3  4   5  6                                 

III.       Trailing zeros are sometimes significant figures. This part makes some people confused. 

            I will try to explain this in very simple way.

            The trailing zeros are significant only if the number is written with a decimal point.

For example

3 4. 5 6 0 0 0  this number has 7 significant numbers because it has a decimal   

1   2   3  4   5  6  7   point between 4 and 5, which means the zeros are significant.

 Without the decimal point (3456000), we have only 4 significant numbers.

Now, let’s put all the information together by solving problems.

Round 53.7285 to four significant figures. The answer is 53.73 ( four s.f)

        

 This number has 6 significant figures, but they ask us to round the number to four significant figures. The fifth digit is 8, which is greater than 5(it is the second rule for rounding off numbers) so the previous number 2 will increase by 1, giving us 3.

Round 23.50343 to three significant figures. The answer is 23.5

           

This number has 7 significant figures, but they ask us to round the number to three significant figures. Look on the fourth digit, which is 0 less than 5, so the previous number 5 will stay the same (this is the first rule for rounding off numbers)                                                                                                                                                                                                                         

Measurements

Measurements are very important in every aspect of our life.

If you are sick, you need to take medication in proper amount. What happen if you take too little or too much? For sure you are not going to get better.

When making a tea, you have to know the proportion of water to the tea bag. Can you imagine putting tea bag in a full pot of water?

Or, when building a fence for your garden, you have to know the length and width of your garden, without this information you wouldn’t know how much material you need to buy for the fence.

Measurements consist of a number and unit, and both are very important.

For example

3 miles or 24 inches

On a basic level, we can place measurements in a few categories: temperature, length, volume, or mass. For example, length we can measure in inches, mile, yards, and feet, but of course is not as easy as it looks. We have another system to express the units; it is called metric system. For example, a length can be measure in millimeters, centimeters, meters, or kilometers.

The problem arrives when we have to convert from one unit of measurement to another. Because I came from Poland, I’m used to the metric system, and I can understand when sometimes Americans have the difficulties to convert the units from the English system to the matric one, as I have the problem to convert the units from matric to English system. Today, I will show you how to do it in a very easy way.

I.              You need to have a conversion factor.

Length

1 meter = 39.37 inches or 1.094 yards or 100 centimeters, or 1000 millimeters

1 kilometer = 0,6214 miles or 1000 meters

1 inch = 2.54 centimeters

1 centimeter = 0.3937 inches

1 mile = 5280 feet

               1 foot = 12 inches

Lets say that you want to know how many kilometers has 34 feet

34 feet	12 inch	1 cm	1 m	1 km
	1 foot	0.3937 inch	100 cm	1000m

1 foot = 12 inches

1 cm = 0.3937

1 m = 100 cm

1 km = 1000m

Remember! You have to choose a conversion factor that cancels the units. In this example, feet canceled with feet, inch with inch, cm with cm and finally we have km.

II. Multiply the numbers in the top section, and then multiply the numbers in the bottom section. After having two answers, the top section has to be divided to the bottom section.

34x12x1x1x1 = 408 – the top section

1x0.3937x100x1000 = 39,370 bottom section

Top section / bottom section; 408 / 39,370 = 0.01036322; writing in scientific notation and rounding off, which I will discus in the next post, we have 1.0 x 10 ^-1  km