Chemistry Calculations

A student calculated a mass to be 250 g, but upon measuring it, found the mass to be 240 g. What is the percent error?

% error= (value accepted- value experimental)/value accepted x 100. % error= (250 g - 240 g)/250 g x 100 = 4%

Isotope Calculation: What is the atomic mass of hafnium if, out of every 500 atoms, 25 have a mass of 176, 95 have a mass of 177, 135 have a mass of 178, 70 have a mass of 179, and 175 have a mass of 180.0?

%=part/whole x 100. %=25/500 x 100= 5%; %=95/500 x 100= 19%; %=135/500 x 100= 27%; %=70/500 x 100= 14%; %=175/500 x 100= 35%. (176 x 5)/100 + (177 x 19)/100 + (178 x 27)/100 + (179 x 14)/100 + (180.0 x 35)/100 = 178.55 amu.

Isotope Calculation: Use the following data to calculate the average atomic mass of "element X" then use the periodic table to identify the element. Isotope: X-16; X-17; X-18. Mass (amu): 15.995; 16.999; 17.999. % Abundance: 99.762; 0.038; 0.20.

(15.995 x 99.762)/100 + (16.999 x 0.038)/100 + (17.999 x 0.20)/100 = 15.999 amu. The element is Oxygen (O).

Write the electron configuration for Tungsten.

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d4

Write the electron configuration for Silver

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d9

Calculate the number of moles in 2.66 x 10^22 atoms of potassium iodide.

2.66 x 10^22 atomsKI= 1 molKI/6.022 x 10^23 atomsKI= 4.42 x 10^-2 molKI.

The orbital speed of Mars is 24.2 km per second. What is its speed in miles/hour?

24.2 km= 0.621 mi x 60 s x 60 min/ 1 s/ 1.00 km/ 1 min/ 1 hour= 5.41 x 10^4 miles/hour.

If a projectile travels 3.00 x 10^3 feet in one second, how far will it travel in 18 minutes?

3.00 x 10^3 ft= 60 s/ 1 s/ 1 min (18 min)= 3.24 x 10^6 feet

Convert 3.5 x 10^6 µm=_________________ hm

3.5 X 10^6 µm= 1 m x 1 hm / 1x10^6 µm/ 100 m= 3.5 x 10^-2 hm.

Convert 5.342 x 10^15 pm=________________ cm

5.342 x 10^15 pm= 1 m x 100 cm / 1 x 10^12 pm/ 1 m = 5.342 x 10^5 cm.

Nuclear Symbol of the following: atomic number 29; mass number 64.

64 29 Cu

If a swimmer swims 85.4 yards in five minutes, how many meters will s/he swim in 70.0 seconds?

85.4 yd= 36 in x 2.54 cm x 1 m x 1 min/ 5 min/ 1 yd/ 1 in/ 100 cm/ 60 s (70 s)= 18.2 m

Give the number of protons, electrons, and neutrons in each of the following atoms. a.) 108 47 Ag b.) 40 20 Ca c.) 23 11 Na

A.) protons= 47; electrons= 47; neutrons= 61. B.) protons= 20; electrons= 20; neutrons= 20 C.) protons= 11; electron= 11; neutrons= 12

A rock has a density of 4 g/mL and a mass of 1.6 x 10^3 mg. What is the volume this rock occupies?

D=m/v. 1.6 x 10^3 mg= 1g/1000mg= 1.6 g. 4 g/mL= 1.6g/v (v) 4v/4= 1.6/4= 0.4 mL Volume= 0.4 mL

A rectangular solid of unknown density is 10 cm long, 2 cm high and 4 cm wide. The mass of this solid is 2.15 x 10^2 g. Find the density of the solid.

Density= m/v. 10 cm x 2 cm x 4 cm = 80 cm^3 2.15 x 10^2 g/ 80 cm^3= 2.69 g/cm^3

Hyphen notation of the following: atomic number 26; mass number 56.

Iron-56

How many molecules are in a 65.6g sample of magnesium chloride.

Molar mass: mmMCl= 24.31 + 2(35.45)= 95.21 g/mol 65.6 gMCl= 1 molMCl x 6.022 x 10^23 moleculesMCl/ 95.21 gMCl/1 molMCl= 4.15 x 10^23 moleculesMCl

What is the mass of 2.53 moles of lead (II) nitrate?

Pb(NO3)2 Molar mass: mmPb(NO3)2= 207.2 + 2(14.01) + 6(16)= 331.22 g/mol 2.53 molPb(NO3)2= 331.22 gPb(NO3)2/1 molPb(NO3)2 =8.38x10^2 gPb(NO3)2

How many protons, electrons, and neutrons is in each of the following isotope? Uranium-235

Protons=92; electrons=92; neutrons=143