# Chemistry Concept Problems

1. (a) Express 50 days in seconds (b) Convert 3.75 meter/sec

to km/hr. Express the results in scientific notation.

2. Perform the following operations and express the answer

with the appropriate number of significant figures.

863[1255-(3.45*10.8)]

3. The recommended dose of Elexophyllin (a drug used to treat

asthma) is 6 mg/kg of body mass. Calculate the dose in milligrams (mg)

required for a 150lb person?

4. Determine the number of protons, neutrons, and electrons

present in (a) an atom of 138Ba (b) 81Br1- (note that the Br atom gains

1 electron to become negatively charged and becomes an anion (Br1-)

5. Magnesium has (3) isotopes with mass numbers 24, 25 and 26

(a) write the chemical symbol of each using the established convention

discussed in class. (b) How many neutrons are present in the nuclide of

each isotope?

6. Write the electron configuration for: (a) H, Li, Na, and K

(b) Be, Mg, and Ca (c) Fe, Ni, and Zn

7. The Chemical formula HNO3 (nitric acid) as written

indicates 1 molecule of HNO3 contains_____________atom(s) of N

and___________ atom(s) of O and a total of_____________atom(s). This

compound is called a ________________compound.

8. The formula weight (molecular weight) of nitric acid

is_____________amus.

9. In the formation of sodium chloride (table salt), the

sodium atom loses an electron and becomes______________charged. The

sodium ion formed is called a_______________. In the process the

chlorine atom gains an electron to become an____________.

10. The mercury concentration in a polluted lake is 0.0125*10 neg 6 mg/L, what is the total mass in kilograms of mercury in the lake is approximately circular with a diameter (d) of 10 miles and average depth (h) of 50 ft? Note that the volume is calculated as follows: V=3.142*(d/2)2*h.

Useful conversion factors: 1000 g=1kg; 1000 mg=1 g

5280 feet=1 mile; 28.317 (L) liters=1 cubic feet

https://brainmass.com/chemistry/general-chemistry/chemistry-concept-problems-127756

#### Solution Preview

1.(a) Express 50 days in seconds (b) Convert 3.75 meter/sec to km/hr. Express the results in scientific notation.

a.50 Days = 50

x 24 hrs = 1200 hrs

x ...

#### Solution Summary

This solution provides an excellent source of practice of chemistry concepts. It helps you solve few basic but important questions from chemistry making your concepts strong.

Chemistry Calculations and Concepts

Determination of the Molar Mass and Ionization Constant of a Weak Monoprotic Acid

Acetic Acid + Water yields Conjugate Base + Hydronium Ion Or HA + H20; H30+ + A-

Calculation of the ionization constant for acetic acid from the measured pH of acetic acid samples:

Acetic Acid titrated with Sodium Hydroxide and the following was determined or known before experiment:

Avg. molar concentration of acetic acid titrated = 0.0455 mol/L

Avg. pH = 3.19

Standardized NaOH = 0.097 mol/L

Mass concentration of acetic acid = 2.4 g/L

Concentration and Ka calculations:

1. Calculation of [H30+] = 10-3.19 = 6.46 X 10-4 ?? - (Is this the way to find the hydronium concentration?)

2. Calculation of [A-] =

3. Calculation of [HA] =

4. Calculation of Ka = [H30+] [A-] =

___________

[HA]

Measurement of the pKa of Acetic Acid by the Half-Neutralization Method

Using half the amount of NaOH required for equilibrium from part 1, the average pH vale was determined to be 4.63

1. Calculation of pKa =

2. Calculation of Ka =

3. Calculation of [H30+] =

4. Calculation of [A-] =

5. Calculation of [HA] =

Molar Mass and Ionization Constant of an Unknown Weak Monoprotic Acid

Unknown acid = 1.84 g/L

NaOH Titrant = 0.097 mol/L

Average pH = 2.60

Avg. molar mass = 0.04252 mol/L

1. Calculation of pKa =

2. Calculation of Ka =

3. Calculation of [H30+] =

4. Calculation of [A-] =

5. Calculation of [HA] =

Problem: OH- concentration of 0.050 M ammonia is 9.5 X 10-4

(a) Write the chemical equation for the dissociation of NH3 in H2O

NH3 + H2O; NH4 + OH-

(b) Equilibrium constant expression for reaction of ammonia with water

Kb = [OH-] [NH4+]

___________

[NH3]

(c) Calculate Kb using the above information

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