Answer:
after 45 days 9 g left
Explanation:
Given data:
Half life Na-24 = 15 days
Mass of sample = 72 g
Mass remain after 45 days = ?
Solution:
Number of half lives passed:
Number of half lives = time elapsed / half life
Number of half lives = 45 days / 15 days
Number of half lives = 3
At time zero total amount = 72 g
After first half life = 72 g/ 2= 36 g
At 2nd half life = 36 g/2 = 18 g
At 3rd half life = 18 g/2 = 9 g
Thus after 45 days 9 g left.
1. Which of the following would be an example of spontaneous
generation?
Answer:
This is the idea of spontaneous generation, an obsolete theory that states that living organisms can originate from inanimate objects. Other common examples of spontaneous generation were that dust creates fleas, maggots arise from rotting meat, and bread or wheat left in a dark corner produces mice
Explanation:
hope you like my answer
Please help if you know please and thanks ;)
Answer:
it takes two hydrogen atoms for every oxygen atom to produce this reaction, so the mole ratio between hydrogen and oxygen is 2:1
What is the mass of 2.53x10^34 atoms of Ni?
Answer:
2.48 g
Explanation:
From the question given above, the following data were obtained:
Number of atoms = 2.53×10³⁴ atoms
Mass of Ni =?
From Avogadro's hypothesis,
we understood that 1 mole of any substance contains 6.02×10²³ atoms.
Therefore, 1 mole of Ni contains 6.02×10²³ atoms.
Recall:
1 mole Ni = 59 g
Therefore, 59 g of Ni contains 6.02×10²³ atoms.
Finally, we shall determine the mass of 2.53×10³⁴ atoms of Ni. This can be obtained as follow:
6.02×10²³ atoms = 59 g
Therefore,
2.53×10³⁴ = 2.53×10³⁴ × 59 / 6.02×10²³
2.53×10³⁴ atoms = 2.48 g
Thus, the mass of 2.53×10³⁴ atoms of Ni is 2.48 g.
Describe how to use a transfer pipet to deliver 10.00 mL of liquid by placing the steps in the correct order.
This question is incomplete, the complete question is;
Describe how to use a transfer pipet to deliver 10.00 mL of liquid by placing the following steps in the correct order;
- Replace the bulb with your index finger and wipe excess liquid off the outside of the pipette.
- Place the tip of the pipette against the side of the beaker and drain the liquid from the pipette until the bottom of the meniscus reaches the calibration mark.
- Transfer the pipette to the receiving vessel.
- Drain the pipette by gravity while holding the tip against the side of the receiving vessel.
- Use a rubber bulb to suck liquid up past the 10.00 ml calibration mark.
- Suck up a third volume of liquid past the 10.00 ml calibration mark.
- Discard the first two pipette volumes of the liquid to rinse the pipette.
Answer:
- Use a rubber bulb to suck liquid up past the 10.00 ml calibration mark.
- Discard the first two pipette volumes of the liquid to rinse the pipette.
- Suck up a third volume of liquid past the 10.00 ml calibration mark.
- Replace the bulb with your index finger and wipe excess liquid off the outside of the pipette.
- Place the tip of the pipette against the side of the beaker and drain the liquid from the pipette until the bottom of the meniscus reaches the calibration mark.
- Transfer the pipette to the receiving vessel.
- Drain the pipette by gravity while holding the tip against the side of the receiving vessel.
Explanation:
First of all, We use a suction device to suck up liquid into pipet. Then we will fill the pipet up to the 10 mL marks and will discard the initial two volumes of liquid and will take a final third volume. We will replace the bulb with index finger and will drain it by placing the tip of pipet at the wall of beaker and drain the liquid.
Arranged in the following steps correctly;
- Use a rubber bulb to suck liquid up past the 10.00 ml calibration mark.
- Discard the first two pipette volumes of the liquid to rinse the pipette.
- Suck up a third volume of liquid past the 10.00 ml calibration mark.
- Replace the bulb with your index finger and wipe excess liquid off the outside of the pipette.
- Place the tip of the pipette against the side of the beaker and drain the liquid from the pipette until the bottom of the meniscus reaches the calibration mark.
- Transfer the pipette to the receiving vessel.
- Drain the pipette by gravity while holding the tip against the side of the receiving vessel.
2 points
A student saw the Moon rise at 6:20 a.m. on Monday. If he wants to see
the Moon rise again on Tuesday, vhat time should he look in the sky?(Mark
the one best answer.)
About 6:20 am
About 6:20pm
About 5:30 am
About 7:10am
what's the pH of a solution composed of 0.2 moles of NH3 and 0.15 moles of nh4cl
Answer:
[tex]pH=4.63[/tex]
Explanation:
Hello!
In this case, since the ionization of ammonia, which is a weak base, is written as:
[tex]NH_3+H_2O\rightleftharpoons NH_4^++OH^-[/tex]
We can see that the ammonium ion is the conjugate acid whereas the hydroxide ions the conjugate base; that is why we use the Henderson-Hasselbach equation to compute the pH, given the pKb of ammonia 4.75:
[tex]pH=pKb+log(\frac{[conj\ acid]}{[base]} )[/tex]
In such a way, for the given moles of ammonia, base, and those of ammonium chloride, conjugate acid form, we obtain:
[tex]pH=4.75+log(\frac{0.15}{0.2} )\\\\pH=4.63[/tex]
Best regards!
Which of the following is the definition of erosion?
A the process that involves The movement Of soil and rock
The process Of disitgration Of rock and soil
Neither
Both
Choose one and explain
Answer:
Neither
Explanation:
None of the answer choices is the correct definition of erosion. Erosion is actually the removal of weathered materials and particle from the surface of rocks and soils.
The process by which rocks and soils are moved is called transportation. The process of disintegration of rocks and soil is called weathering.Erosion is a serious problem in Agriculture as it removes rich and fertile soil cover. This therefore renders the soil barren and stripped of available nutrients.
Answer:
The process of breaking down rock and soil.
Explanation:
Why did the French set up trading posts in North America?
Answer: Their main aim was to provide goods, specifically furs and sugar exportation.
Explanation:
can you make energy with ionized particles? yes or no and how
Many reactions double their rates with every ten degrees rise in temperature. Assume that such a reaction takes place at 301 K and 311 K. What must its activation energy be for this statement to hold
Answer:
57.6 KJ/mol
Explanation:
We have that;
T1 = 301 K
T2= 311 K
k1 = k1
k2= 2k1
R = 8.314 JK-1
Ea= ?
So;
ln(k1/k2) = (-Ea/R) (1/T1 - 1/T2)
ln (k1/2k1) = -(Ea/8.314) (1/301 - 1/311)
ln(1/2) = -(Ea/8.314) (3.3 * 10^-3 - 3.2 * 10^-3)
-0.693 = -(Ea/8.314) 0.1 * 10^-3
-0.693/ 0.1 * 10^-3 = -(Ea/8.314)
-6930 = -(Ea/8.314)
Ea = 6930 * 8.314
Ea = 57.6 KJ/mol
which type of organism carries out cellular respiration
Answer:Prokaryotic cells carry out cellular respiration within the cytoplasm and eukaryotic cells carry out respiration in the mitochondria
Explanation:
For all seawater problems, assume the salinity is 3.5%
If you have a 2000 gram sample of seawater, how many grams of pure water are there?
0.035 x 2000) = x, 2000 - x = pure water
Answer to the nearest WHOLE number.
Answer:
1930g
Explanation:
We have been given that the salinity of sea water is 3.5%;
Now the mass of sea water sample is 2000g
So, problem here is to find the quantity of pure water in the sample = ?
Solution:
Let us find the quantity of the salt in the sample;
Salt content = 3.5% x 2000 = 70g
Amount of pure water = 2000 - 70 = 1930g
Write a balanced equation describing the reduction of H2SeO4 by SO2 to produce selenium. (Use the lowest possible coefficients. Include states-of-matter under SATP conditions in your answer.)
Answer:
[tex]\mathbf{H_2SeO_{4(aq)} + 3SO_{2(aq)} + 2H_2O_{(l) } \to Se_{(s)} + 3H_2SO_{4(aq)} }[/tex]
Explanation:
We are to write a balanced equation from the information given above by including the states of their matter according to SATP conditions;
[tex]\mathbf{H_2SeO_{4(aq)} + 3SO_{2(aq)} + 2H_2O_{(l) } \to Se_{(s)} + 3H_2SO_{4(aq)} }[/tex]
From above;
The oxidizing agent is [tex]\mathbf{H_2SeO_{4(aq)} }[/tex]
The reducing agent is [tex]\mathbf{SO_{2(aq)} }[/tex]
When a chemical change occurs _____.
Need ASAP please someone
Select one:
a. atoms are rearranged
b. the law of conservation of mass is always obeyed
c. the chemical properties of new substances are different from the ones you started with
d. all of these
Answer:
d
Explanation:
i think its d but im not sure.
HEY THIS ANSWER CORRECT ?
Answer:
I don't think that answer is right. I got 543.04 grams.
Explanation:
I think the question is asking for grams in the samlpe instead of the moles in the sample because it already gives you the amount of moles.
How many moles are in 563.9 grams of arsenic?
Answer:
No. of moles, n = 7.52 moles
Explanation:
Given that,
Mass, m = 563.9 grams
Molar mass of arsenic = 74.92 g/mol
We need to find the number of moles in 563.9 grams of arsenic. Let it is denoted by n. It is equal to given mass divided by total molar mass.
[tex]n=\dfrac{563.9 }{74.92}\\\\=7.52\ \text{moles}[/tex]
So, there are 7.52 moles in 563.9 grams of arsenic.
At equilibrium the reactant and product concentrations are constant because a change in one direction is balanced by a change in the other as the forward and reverse rates become equal: (MTS 5/5/2018) When a chemical system is at equilibrium, Group of answer choices the concentrations of the reactants and products have reached constant values. the concentrations of the reactants are equal to the concentrations of the products. the forward and reverse reactions have stopped. the reaction quotient, Q, has reached a maximum. None of the choices.
Answer:
concentrations of the reactants and products have reached constant values
Explanation:
When a reaction is carried out in a closed system, it attains dynamic equilibrium after sometime. We define dynamic equilibrium as a situation in which the forward and reverse reactions proceed at the same rate.
When this occurs, the concentration of the reactants and products remain fairly constant. Hence the answer.