Chemistry Questions

The half-life of cesium-137 is 30 years. Suppose we have a 180 mg sample. Find the mass that remains after t years. Let y(t) be the mass (in mg) remaining after t years. Then we know the following. y ( t ) = y ( 0 ) e k t = ⋅ e k t Since the half-life is 30 years, then y ( 30 ) = mg. Thus, e 30 k = . Therefore, k = . Now, remembering that ln x n = n ln x and that e ln z = z , we have y ( t ) = 180 e ( t / 30 ) ( − ln 2 ) = mg. How much of the sample remains after 70 years? After 70 years we have the following. y ( 70 ) = 180 ⋅ 2 = mg (Round your answer to two decimal places.) After how long will only 1 mg remain? To find the time at which only 1 mg remains, we must solve 1 = y ( t ) = 180 ( 2 − t / 30 ) , and so we get the following. t = − 30 log 2 ( ) Hence, we conclude the following. t = yr (Round your final answer to one decimal place.)
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Suppose you start with 0.303 g of copper wire and faithfully follow the procedure. At the end you find that the copper dust weighs 0.309 g. Based on your understanding of the experimental procedure, offer at least two rational explanations for this apparent violation of the law of conservation of mass.
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The equilibrium constant for the reaction below, at a given temperature is 45.6. If the equilibrium concentrations of F2 and BrF3 are 1.24 x 10-1 M and 1.99 x 10-1 M respectively, calculate the equilibrium concentration of Br2. (4)
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The unsaturated hydrocarbon butadiene (C4H6) dimerizes to 4-vinylcyclohexan (C8H12).When data collected in studies of the kinetics of this reaction were plotted against reaction time, plots of [C4H6] or ln[C4H6] produced curved lines, but the plot of 1/[C4H6] was linear.a) What is the rate law for the reaction?b) How many half-lives will it take for the [C4H6] to decrease to 3.1% of its original concentration? The relationship of [A]t/[A]o = 0.50^n, where n = the number of half-lives.
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1 Point What is the temperature in kelvins of 23°C? O A. 11.9K O B. 6279K OC. 296K O D. 250k
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Which of these factors make hydrogen fuel cells a better option than burning fossil fuels
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In the equation below, identify the Brønsted-Lowry acid, Brønsted-Lowry base, conjugate acid, conjugate base. NH4+(aq) + NO-2 (aq) = HNO2(aq) +NH3(aq)
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Which example of transportation most likely involves the widest variety of vehicles? A. Blood is rushed from a blood bank to a local hospital. B. Fresh vegetables are transported from a farm to a nearby city. C. science textbook is transported from a printer in China to your school, and then to your home. D. Gravel from a gravel pit is transported to construction sites across the state.
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Provide structures for the products obtained by the reaction of propanal under five conditions outlined below. 1. Sodium Borohydride followed by work up. [A] 2. Methyl lithium followed by work up. [B] 3. Isopropyl magnesium bromide followed by work up. [C] 4. Methyl triphenylphosphonium bromide and a base. [D] 5. Two equivalents of methanol in the presence of an acid catalyst. [E] 6. Zinc amalgam and hydrochloric acid. [F]
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Bicycles- How do different forms of transportation meet people’s transportation needs?
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Kf(water) = -1.86 °C/m In a laboratory experiment, students synthesized a new compound and found that when 13.39 grams of the compound were dissolved in 202.1 grams of water, the solution began to freeze at -2.050 °C. The compound was also found to be nonvolatile and a non-electrolyte. What is the molecular weight they determined for this compound ?
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Lab Report: Factors Affecting Solution Formation 1. On the basis of your results, what is the relationship between the temperature of the solvent and the solubility of KCl and KClO3 (Show the both graphs)? 2. Provide the two unknowns A and B and describe how you determined the identity using your data. 3. Explain three factors the affect how fast substances dissolve. PLEASE HELP ME WITH THESE QUESTIONS
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A chemistry teacher adds 50.0 mL of 1.50 M H2SO4 solution to 200 mL of water. What is the concentration of the final solution? Use M subscript i V subscript i equals M subscript f V subscript f.. 0.300 M 0.375 M 6.00 M 7.50 M
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Oh no! The thermometer punctured a hole in the bottom of the coffee cup, and water is spilling out. Check all actions you would take. Throw the broken pieces away. Use the punctured cup as the outside cup, not the inside cup. 0 Replace the cup O Clean the area | Mention the spill to the teacher. O Call 9-1-1
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If a reaction mixture contains 3 moles of O2(g) with 4 moles of H2(g), which reactant is the limiting reactant and what is the mass (in grams) remaining of the reactant in excess?
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If a solution containing 53.99 g 53.99 g of mercury(II) nitrate is allowed to react completely with a solution containing 9.718 g 9.718 g of sodium sulfide, how many grams of solid precipitate will form?
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Write the Ka expression for an aqueous solution of hypochlorous acid: (Note that either the numerator or denominator may contain more than one chemical species. Enter the complete numerator in the top box and the complete denominator in the bottom box. Remember to write the hydronium ion out as H3O+ , and not as H+) Ka= _______________
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Consider the following multistep reaction: A+B→AB(slow) A+AB→A2B(fast)–––––––––––––––––––– 2A+B→A2B(overall) Based on this mechanism, determine the rate law for the overall reaction. Express your answer in standard MasteringChemistry format. For example, if the rate law is k[A]3[B]2 type k*[A]^3*[B]^2. View Available Hint(s)
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Jaynes science teacher mixed a clear liquid with a blue liquid in a beaker. After a few minutes there was a white solid at the bottom of the beaker. What mostly likely true about white solid
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Find how many milliliters of NaOH should be used to reach the half-equivalence point during the titration of 20.00 mL 0.888 M butanoic acid, CH3CH2CH2COOH (Ka = 1.54×10–5) with 0.425 M NaOH solution. Enter 2 decimal places.
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What is the molarity of a solution that contains 148g NaOH in 4.00 L solution? a 0.925 M b 0.0253 M c 0.459 M d 1.363 M
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1. Which is not an example of a physical change to a wooden stick? A) slicing wood shavings from the stick B) bending the stick back and forth C) burning the stick D) chopping the stick in half
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For a different reaction, Kc = 1.39, kf=12.6s−1 , and kr= 9.08 s−1 . Adding a catalyst increases the forward rate constant to 4.28×103 s−1 . What is the new value of the reverse reaction constant, kr, after adding catalyst?
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Compute diffusion coefficients for the interdiffusion of carbon in both (a) α-iron (BCC) and (b) γ-iron (FCC) at 1000˚C. Assume that D0 for the interdiffusion of carbon in α-iron and in γ-iron are 1.1 × 10-6 and 2.3 × 10-5 m2/s, respectively, and that Qd are 80 and 148 kJ/mol, respectively.
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