1answer.
Ask question
Login Signup
Ask question
All categories
  • English
  • Mathematics
  • Social Studies
  • Business
  • History
  • Health
  • Geography
  • Biology
  • Physics
  • Chemistry
  • Computers and Technology
  • Arts
  • World Languages
  • Spanish
  • French
  • German
  • Advanced Placement (AP)
  • SAT
  • Medicine
  • Law
  • Engineering
andrew-mc [135]
3 years ago
5

One question please help!

Chemistry
1 answer:
Agata [3.3K]3 years ago
3 0
<span>1 trial : you have nothing to compare the result with - you don't know if it's a mistake.
2 trials : you can compare results - if very different, one may have gone wrong, but which one?
3 trials : if 2 results are close and 3rd far away, 3rd probably unreliable and can be rejected.

******************************

First calculate the enthalpy of fusion. M, C and m,c = mass and specific heat of calorimeter and water; n, L = mass and heat of fusion of ice; T = temperature fall.

L = (mc+MC)T/n.

c=4.18 J/gK. I assume calorimeter was copper, so C=0.385 J/gK.

1. M = 409g, m = 45g. T = 22c, n = 14g
L = (45*4.18+409*0.385)*22/14 = 543.0 J/g.

2. M = 409g, m = 49g, T = 20c, n = 13g
L = (49*4.18+409*0.385)*20/13 = 557.4 J/g.

3. M = 409g, m = 54g, T = 20c, n = 14g
L = (54*4.18+409*0.385)*20/14 = 547.4 J/g.

(i) Estimate error in L from spread of 3 results.
Average L = 549.3 J/g.
average of squared differences (variance) = (6.236^2+8.095^2+1.859^2)/3 = 35.96
standard deviation = 5.9964
standard error = SD/(N-1) = 5.9964/2 = 3 J/g approx.

% error = 3/547 x 100% = 0.5%.

(ii) Estimate error in L from accuracy of measurements:
error in masses = +/-0.5g
error in T = +/-0.5c

For Trial 3
M = 409g, error = 0.5g
m = 463-409, error = sqrt(0.5^2+0.5^2) = 0.5*sqrt(2)
n =(516-463)-(448-409)=14, error = 0.5*sqrt(4) = 1.0g
K = (mc+MC)=383, error = sqrt[2*(0.5*4.18)^2+(0.5*0.385)^2] = 2.962

L = K*T/n
% errors are
K: 3/383 x 100% = 0.77
T: 0.5/20 x 100% = 2.5
n: 1.0/14 x 100% = 7.14

% errors in K and T are << error in n, so we can ignore them.
% error in L = same as in n = 7% x 547.4 = 40 (always round final error to 1 sig fig).

*************************************

The result is (i) L= 549 +/- 3 J/g or (ii) L = 550 +/- 40 J/g.
Both are very far above accepted figure of 334 J/g, so there is at least one systematic error in the experiment or the calculations.
eg calorimeter may not be copper, so C is not 0.385 J/gK. (If it was polystyrene, which absorbs/ transmits little heat, the effective value of C would be very low, reducing L.)
Using +/- 40 is probably best (more cautious).
However, the spread in the actual results is much smaller; try to explain this discrepancy - eg
* measurements were "fiddled" to get better results; other Trials were made but only best 3 were chosen.
* measurements were more accurate than I assumed (eg masses to nearest 0.1g but rounded to 1g when written down).

Other sources of error:
L=(mc+MC)T/n is too high, so n (ice melted) may be too small, or T (temp fall) too high - why?
* it is suspicious that all final temperatures were 0c - was this actually measured or just guessed? a higher final temp would reduce L.
* we have assumed initial and final temperature of ice was 0c, it may actually have been colder, so less ice would melt - this could explain small values of n
* some water might have been left in container when unmelted ice was weighed (eg clinging to ice) - again this could explain small n;
* poor insulation - heat gained from surroundings, melting more ice, increasing n - but this would reduce measured L below 334 J/g not increase it.
* calorimeter still cold from last trial when next one started, not given time to reach same temperature as water - this would reduce n.
Hope This Helps :)
</span>
You might be interested in
Water sits in an open beaker. assuming constant temperature and pressure, the vapor pressure of the water ______________ as the
user100 [1]

For a given system, vapor pressure can be defined as the pressure exerted by the vapor phase in equilibrium with the condensed phase.

In this case, as water sits in an open beaker it tends to evaporate thereby forming water vapor. This vapor phase then exerts a pressure over the liquid water, which is termed as the vapor pressure of water at that temperature and pressure. As water continues to evaporate, more and more molecules escape into the vapor phase which thereby increases the vapor pressure.

Ans: The vapor pressure of water increases as the water evaporates.

3 0
3 years ago
you go out to dinner and the bill comes to $35.51. how much should you tip if you want the tip to be 20% of the bill.​
agasfer [191]
35.51 times 0.2 is 7.102
So you should tip $7.102
8 0
3 years ago
Read 2 more answers
How many atoms are in two water molecules? pls and thxxxxxxxxx
arlik [135]

Answer:

A water molecule consists of three atoms; an oxygen atom and two hydrogen atoms, which are bond together like little magnets. The atoms consist of matter that has a nucleus in the centre. one mole of water contains 6.02 x 1023 MOLECULES of water But each molecule of water contains 2 H and 1 O atom = 3 atoms, so there are approximately 1.8 x 1024 atoms in a mole of water.Feb 12, 2003

Explanation:

7 0
3 years ago
Consider the reaction. 2 Pb ( s ) + O 2 ( g ) ⟶ 2 PbO ( s ) An excess of oxygen reacts with 451.4 g of lead, forming 367.5 g of
Art [367]

Answer : The percent yield of the reaction is, 75.6 %

Solution : Given,

Mass of Pb = 451.4 g

Molar mass of Pb = 207 g/mole

Molar mass of PbO = 223 g/mole

First we have to calculate the moles of Pb.

\text{ Moles of }Pb=\frac{\text{ Mass of }Pb}{\text{ Molar mass of }Pb}=\frac{451.4g}{207g/mole}=2.18moles

Now we have to calculate the moles of PbO

The balanced chemical reaction is,

2Pb(s)+O_2(g)\rightarrow 2PbO(s)

From the reaction, we conclude that

As, 2 mole of Pb react to give 2 mole of PbO

So, 2.18 mole of Pb react to give 2.18 mole of PbO

Now we have to calculate the mass of PbO

\text{ Mass of }PbO=\text{ Moles of }PbO\times \text{ Molar mass of }PbO

\text{ Mass of }PbO=(2.18moles)\times (223g/mole)=486.1g

Theoretical yield of PbO = 486.1 g

Experimental yield of PbO = 367.5 g

Now we have to calculate the percent yield of the reaction.

\% \text{ yield of the reaction}=\frac{\text{ Experimental yield of }PbO}{\text{ Theoretical yield of }PbO}\times 100

\% \text{ yield of the reaction}=\frac{367.5g}{486.1g}\times 100=75.6\%

Therefore, the percent yield of the reaction is, 75.6 %

3 0
3 years ago
Give examples to three solutions you commonly use and identify the solvent and solutes that make it each up.
8_murik_8 [283]
Mouthwash:
solvent - water
solute - alcohols

vinegar:
solvent - water
solute - acetic acid

bleach:
solvent - water
solute - sodium hypochlorite

hope this helps!!

8 0
3 years ago
Read 2 more answers
Other questions:
  • Which substance is a gas at room temperature and atmospheric pressure?
    14·1 answer
  • Which group of elements ,in the periodic table, would most likely be used for electrical wires?
    7·1 answer
  • In your own words, give a summary of the history of the atom. Make sure to use names of models and the scientists associated wit
    8·2 answers
  • Which is the atomic number of an alkali metal? <br> 10<br> 11<br> 12<br> 13
    12·2 answers
  • 200 feet in 30 seconds is what speed?
    15·2 answers
  • If 747 joules of energy is added to a sample of aluminum (specific heat capacity = 0.899 J/g*C) and the temperature goes up from
    8·1 answer
  • Fill in the coefficients that will balance the following reaction:
    11·1 answer
  • Advantages of artificial fertilizers?
    14·1 answer
  • Which explanation describes why seafloor spreading occurs?
    8·2 answers
  • 1.Calculate the mass of compound required to prepare 100.00 mL of a 1.40x10-2M CuCl2.Show your work.
    15·1 answer
Add answer
Login
Not registered? Fast signup
Signup
Login Signup
Ask question!