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2 years ago

Which fraction of an original 20.00-gram sample of nitrogen-16 remains unchanged after 35.65 seconds?

2 answers:

4 0

Approximately 1/32 grams of the original sample of 20.00 grams of nitrogen-16 would remain unchanged after 35.65 seconds

Genrish500 [490]2 years ago

4 0

Answer:

1/32 = 0.03125 = 3.125%

Explanation:

The nitrogen-16 is an unstable isotope of nitrogen. The isotopes are the elements with the same atomic number but have a different number of mass. It means that they have a different number of neutrons (mass = protons + neutrons).

Because it is unstable, it decays in particles beta(β) and alpha (α), and the time that is necessary to the half of the mass disappear is called half-life which is equal to 7.13 s for nitrogen-16.

The mass that remains (m) can be calculated by:

m = m0/2ˣ, where m0 is the initial mass, and x the number of half-lives.

x = time/half-life time

x = 35.65/7.13

x = 5

Then,

m = 20.00/2⁵

m = 20.00/32

m = 0.625 g

The fraction is the mass that remains divided by the original mass:

0.625/20.00 = 1/32 = 0.03125 = 3.125%

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A chemist mixes 75.0 g of an unknown substance at 96.5C w/ 1,150 g of water at 25.0C . if the final temperature of the system is

vichka [17]

Remember: heat lost = heat gained

When calculating heat loss or gain, remember

mass*(spec heat cap)*(change in T)

The unknown loses heat- we don't know the spec heat cap, so we'll call it x.

The water gains. I've omitted the units, but always use when solving problems on your own.

75*x*(96.5-37.1) = 1150*4.184*(37.1-25)

Now it's all set up- use algebra to get x, the spec heat cap of the unk in J/g*degC

I hope my answer has come to your help. Thank you for posting your question here in Brainly. We hope to answer more of your questions and inquiries soon. Have a nice day ahead!

3 0

2 years ago

Which two rocks are primarily composed of a mineral that bubbles with acid?

Marianna [84]

To most geologists, the term "acid test" means placing a drop of dilute (5% to 10%) hydrochloric acid on a rock or mineral and watching for bubbles of carbon dioxide gas to be released. The bubbles signal the presence of carbonate minerals such ascalcite, dolomite, or one of the minerals listed in Table 1.

8 0

2 years ago

Before landing, the brakes and the tires of an airliner have a temperature of 15.0∘C. Upon landing, the 90.7 kg carbon fiber bra

Goryan [66]

Answer:

0.921 J/g degrees C

Explanation:

Recall that the First Law of Thermodynamics demands that the total internal energy of an isolated system must remain constant. Any amount of energy lost by the brakes must be gained by the tires (in the form of heat in this situation). Therefore, heat given off by the brakes = −heat taken in by tires, or:

−qbrakes=qtires

The equation used to calculate the quantity of heat energy exchanged in this process is:

−qbrakes=−cbrakes mbrakes ΔTbrakes=ctires mtires ΔTtires=qtires

First we must convert the mass of the tires and the brakes from kg to g.

massbrakes=90.7 kg×1,000. g1 kg=9.07×104 g

masstires=123 kg×1,000. g1 kg=1.23×105 g

Next, substitute in known values and rearrange to solve for ctires. Note that the final temperature for both the tires and the brakes is 172∘C, the initial temperature of the brakes is 312∘C and the initial temperature of the tires is 15∘C.

−(1.400Jg∘C)(9.07×104 g)(172∘C−312∘C)=(ctires)(1.23×105 g)(172∘C−15∘C)

ctires=−(1.400 Jg∘C)(9.07×104 g)(−140∘C)(1.23×105 g)(157∘C)=17,777,200 J19311000 g∘C=0.9206Jg∘C

The answer should have three significant figures, so round to 0.921Jg∘C.

6 0

2 years ago

During a lab experiment performed at STP conditions, you prepare HCl by reacting 100. ml of Cl2 gas with an excess of H2 gas.

Brrunno [24]

Answer: 19.4 mL Ba(OH)2

Explanation:

H2(g) + Cl2(g) --> 2HCl(aq) (make sure this equation is balanced first)

At STP, 1 mol gas = 22.4 L gas. Use this conversion factor to convert the 100. mL of Cl2 to moles.

0.100 L Cl2 • (1 mol / 22.4 L) = 0.00446 mol Cl2

Use the mole ratio of 2 mol HCl for every 1 mol Cl2 to find moles of HCl produced.

0.00446 mol Cl2 • (2 mol HCl / 1 mol Cl2) = 0.00892 mol HCl

HCl is a strong acid and Ba(OH)2 is a strong base so both will completely ionize to release H+ and OH- respectively. You need 0.00892 mol OH- to neutralize all of the HCl. Note that one mole of Ba(OH)2 contains 2 moles of OH-.

0.00892 mol OH- • (1 mol Ba(OH)2 / 2 mol OH-) • (1 L Ba(OH)2 / 0.230 M Ba(OH)2) = 0.0194 L = 19.4 mL Ba(OH)2

3 0

2 years ago

A 0.20 mol sample of MgCl2(s) and a 0.10 mol sample of KCl(s) are dissolved in water and diluted to 500 mL. What is the concentr

igor_vitrenko [27]

Answer:

1 M

Explanation:

Magnesium chloride will furnish chloride ions as:

$MgCl_2\rightarrow Mg^{2+}+2Cl^-$