Chem 1110 Exam 1 Chapters 1 and 2

How many significant figures are in 7079?

4

Express 4.10x10^4 megameters in meters

4.10x10^10 because mega is 10^6

How many moles are in 8.022x10^23 atoms of a given sample?

1.332 moles. There are 6.022x10^23 atoms in each mole. We know this from Avogadro's Constant (you will be given this number on the exam). Divide the given atoms by Avogadro's number. 8.022x10^23 x 6.022x10^23=1.332 moles

How many moles are in 94.97 g of Be?

10.54 moles. For one mole of Be, there is 9.0122 grams. We know this because this is the atomic weight/mass number in the periodic table. Divide 94.97g by the mass number found on the periodic table. 94.97g/9.0122g=10.54 moles

What is the mass, in grams, of 7.540x10^23 atoms of B?

13.536 grams. There are 6.022x10^23 atoms in 10.811g of B (Boron). This number is found by looking at the atomic mass number for Boron on the periodic table. Multiply the given atoms by the atomic mass number of Boron, then divide by Avogadro's number, 7.540x10^23 x 10.811 / 6.022x10^23 = 13.536 grams.

Express 2.14x10^3 picograms in micrograms

2.14x10^-3 because pico is 10^-12 and micro is 10^-3

How many atoms are in (9.410x10^2) g of F?

2.983x10^25 atoms. There are 6.022x10^23 atoms in 18.998g of F. We know this from the mass number given by the periodic table for F (fluorine) Multiply the given atoms by Avogadro's number, and divide by the atomic mass number. 9.410x10^2 x 6.022x10^23 / 18.998 = 2.983x10^25 atoms.

An object exerts a pressure of 3.61 lb/cm2. What is the pressure exerted by the object in lb/in2? 1 in ≡ 2.54 cm.

23.3 lb/in^2 because 3.61lb/1cm^2 x (2.54cm/1in)^2 = 23.3 ln/in^2. The 2.54 is squared because the final unit inches, is also squared.

A celestial object is analyzed for magnesium composition and is found to have a very different isotope distribution of the three stable isotopes of magnesium: 24Mg (23.9850 amu, 40.54%); 25Mg (24.9858 amu, 18.06%); and 26Mg (25.9826 amu). What is the atomic mass of Mg, in amu, in this celestial object?

24.99 amu. Multiply each amu by the percent, Ex, 23.9850x0.4054. Do this for all of them. 26Mg does not have a percent because it is the rest of the percentage. Add the other percentages up, then subtract that from 100. 40.54+18.06=58.6. 100-58.6=41.4 This is the percent for 26Mg. Once you multiply all of these by their percentages, add them up. You will get 24.99.

An atom of strontium-90 has a charge of +2. How many protons, neutrons, and electrons, respectively, make up this atom?

38 Protons, 52 neutrons, 36 electrons. Protons can be found by looking at the periodic table, Sr is number 38. Neutrons can be found by the 90 in the name. If there is 38 protons, then there is 52 neutrons because 38 + 52 is 90. Electrons can be found by the +2 charge. The charge is found by subtracting protons from electrons so 38 - 36 = +2

What is the mass, in grams, of 0.5365 moles of Be?

4.8349g. For one mole of Be, there is 9.0122 grams. We know this because of the atomic mass found on the periodic table. Multiply the given moles by the atomic mass number, 0.5365x9.0122=4.8349g

How many significant figures are in 0.0050010?

5

How many atoms are in (8.57x10^-1) moles of a substance?

5.16x10^23 atoms. There are 6.022x10^23 atoms in each mole. We know this from Avogadro's Constant (you will be given this number on the exam). Multiply the given atoms by Avogadro's constant. 8.57x10^-1 x 6.022x10^23 = 5.16x10^23 atoms

Chromium occurs naturally as only four isotopes: 50Cr (49.95 amu, 4.345% abundance); 52Cr (51.94 amu, 83.789% abundance); 53Cr (52.94 amu, 9.501% abundance); and 54Cr (2.365% abundance). Using the atomic mass of chromium from the periodic table, what is the mass of the 54Cr isotope in amu?

54.12 amu. Multiply each amu by their percentage. Ex, 49.95x0.04345=2.170. for 54Cr you see there is no amu. You have to see the trend for each amu. For 50Cr it is 49.95, for 52Cr it is 51.94, for 53Cr it is 52.94. You can see that the amu raises up by one for each isotope. If this is true, the 54Cr amu is 53.94. Multiply this by its percentage and add this number to the other numbers you got from multiplying the others by their percentages. You will get 54.12.

How many significant figures are in 1.05010?

6

Express 6.28x10^2 liters in centiliters

6.28x10^4 because centi is 10^-2

Boron occurs only in two isotopes: 10B (10.01 amu) and 11B (11.01 amu). If the atomic mass of boron in a particular meteorite is 10.69 amu, what is the percent abundance of 11B in the sample?

68%. This is found by substitution. the equation, 10.69amu=10.01x+11.01x, where x = percent abundance. For the abundance that you are not looking for, make that (1-x). The equation should look like 10.69=10.01(1-x)+11.01x. Solve for x. You should get x = 0.68, multiply this by 100 because it is a percentage. You will get 68%

An object is travelling at 40.0 meters per second. What is the velocity of the object in miles per hour? 1 km = 0.62137 mile.

89.5 mph because 40m/1sec x 60sec/1min x 60min/1hr x 1km/10^3m = 144 x 0.62137 = 89.5

How can you tell if a nuclide is stable?

Divide the atomic mass (aka the bigger number) by the smaller number (aka the atomic number/number of protons). If the number you get from dividing that isn't 1, 1.25, or 1.5 it is likely unstable. If the atomic number is above 82. It is automictically unstable.

What group are the Alkali Metals in?

Group 1 or 1A

What group are the Halogens in?

Group 17 or 7A

What group are the Noble (inert) Gases in?

Group 18 or 8A

What group are the Alkali Earth Metals in?

Group 2 or 2A

Intensive Properties

Properties that are independent of amount of substance present. These are Temperature and Density

What charge does an Electron have?

negative charge

What charge does a Neutron have?

neutral charge

What charge does a Proton have?

positive charge

Extensive Properties

properties that are dependent on the amount of substance present. These are Mass and Volume