How do i solve the following problems

Question

I need help calculating this and please explain

 

 

1) An explosion occurs at the end of a pier. A person standing at the other end of the pier hears the loud noise after 364 milliseconds. If sound travels through air at a speed of 343 m/s, how many feet away from the explosion was the person?

 

2) How many moles of calcium nitrate are present in a 75.32 g sample?

3)How many grams of calciu, are present in a 75.32 g sample of Ca(NO3)2?

4) What is the mass percentcalcium in the above sample?

 

 

 

 

Answer 1

Hello J - 

 

1. If velocity is distance/time, then distance is velocity*time.

 

So 343 m/sec * 3.2 ft/m *.346 sec = 399.5 ft. The length of the pier, assuming you could measure time to the millisecond. This makes sense since in about 1/3 of a second the sound going at 1125 ft/sec should be about 400 ft.

 

2. Ca atomic weight is 40.08. N atomic weight is 14.007, O is 15.9964.

So with 1 Ca, 2 N, and 6 O a mole would be 164.072 g. So the number of moles Ca(NO₃)₂ in 75.32 g is 75.32/164.072 or 0.459 moles.

 

3. Since one atom of Ca is in every molecule of Calcium Nitrate, the number of moles of calcium is also 0.459 moles.

 

4. This is just the Ca contribution to the total molecular mass. So 40.08/164.072 * 100 or 24.43 %

 

Hope this helps you.

 

Ken

 

Answer 2

#1 is within my knowledge.

 

d = r · t

d = 343m/sec · 364 milliseconds

 

Conversion of units needed.

1 meter = 3.28 feet

1000 milliseconds = 1 second

 

d = 343m/sec · 3.28ft/m · 364 milliseconds · 1sec/1000 milliseconds

 

To determine if the numbers are in the numerator or the deminator, place the units so that they reduce out leaving only the desired unit, in this case feet.

 

d = 343 · 3.28ft / 1000

 

d= 1.12504

 

The explosion was 1.12504 feet from the person.