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Questions in chemistry

[Answered] Juliet started working with a radioactive substance. In 1997, she started with 200 g. When she measured again in 2002, she had 100 g left. In 2007, she had 50 g. | Radioactive isotope | Half-life | |---|---| | Rubidium-91 | 58.4 seconds | | lodine-131 | 8 days | | Cobalt-60 | 5 years | | Carbon-14 | 5730 years | | Cesium-135 | $2.3 \times 10^6$ years | | Uranium-238 | $4.5 \times 10^9$ years | Which substance is she most likely measuring? A. rubidium-91 B. iodine-131 C. cobalt-60 D. carbon-14

[Answered] What causes atoms to react with each other? A. A state change B. A chemical equation C. A chemical reaction D. A physical change

[Answered] A student separates salt from a mixture of salt and sand. What is the correct order of steps for the student to take? A) filter -> evaporate -> shake with water B) filter -> shake with water -> evaporate C) shake with water -> evaporate -> filter D) shake with water -> filter -> evaporate

[Answered] Manganese dioxide [tex]$\left( MnO _2(s), \Delta H_{ f }=-520.0 kJ\right)$[/tex] reacts with aluminum to form aluminum oxide [tex]$\left( Al _2 O _3(s), \Delta H_{ f }=-\right.$[/tex] [tex]$1699.8 kJ / mol$[/tex]) and manganese according to the equation below. [tex]$3 MnO_2(s)+4 Ar(s) \rightarrow 2 Al_2 O_3(g)+3 Mn(s)$[/tex] What is the enthalpy of the reaction? Use [tex]$\Delta H_{r \times n}=\sum\left(\Delta H_{\text {teproducts }}\right)-\sum\left(\Delta H_{\text {tereatants }}\right)$[/tex]

[Answered] In the combustion of propane, $C_3H_8$, 32 g of $O_2$ is needed to form 10 g of $H_2O$. What are the theoretical yield and percentage yield of $H_2O$? ($C = 12, O = 16, H = 1$) $C_3H_8(g) + 5O_2(g) \longrightarrow 3CO_2(g) + 4H_2O(1)$

[Answered] 1. From the following ionic equations below, put a tick (✓) if there is a reaction taking place and an x if there is no reaction taking place. a. [tex]Zn ^{2+}( aq )+ Fe ( s ) \longrightarrow Fe ^{2+}(\frac{ aq }{ a })+ Zn ( s )[/tex] b. [tex]Mg ^{2+}( aq )+ Zn ( s ) \longrightarrow Zn ^{2+}( aq )+ Mg ( s )[/tex] c. [tex]Fe ^{2+}( aq )+ Zn ( s ) \longrightarrow Zn ^{2+}( aq )+ Fe ( s )[/tex] d. [tex]Pn ^{2+}( aq )+ Cu ( s ) \longrightarrow Cu ^{2+}( aqu ) ! Pu ( s )[/tex] e. [tex]Cu ^{2+}( aq )+ Fe ( s ) \longrightarrow Fe ^{2+}( aq )+ Cu ( s )[/tex] 2. Define spectator ion.

[Answered] When using chemicals, such as coil cleaner, the technician should always do which of the following? A. Review chemical Material Safety Data Sheet (MSDS) B. Wear skin protection C. All answers presented D. Wear safety goggles

[Answered] B. Name the separation method for the following: 1. Salt from sea water 2. Oil from water 3. Tea leaves from tea 4. Cream from milk 5. Wheat grains from husk

[Answered] Which statement best describes balancing equations and the law of conservation of mass? A. There are more atoms in the reactants than in the products, and the total mass is the same in the reactants and in the products. B. The number of atoms is the same in the reactants and in the products, and the total mass is the same in the reactants and in the products. C. There are fewer atoms in the reactants than in the products, and the total mass is less in the reactants than in the products. D. There are more atoms in the reactants than in the products, and the total mass is higher in the reactants than in the products.

[Answered] Magnesium metal reacts with dilute hydrochloric acid to produce magnesium chloride and hydrogen. The chemical equation for the reaction is shown below. [tex]Mg(s)+2 HCl(aq) \longrightarrow MgCl_2(aq)+H_2(g)[/tex] Starting with the known mass, 12.0 g of Mg, calculate the following: (a) the mass of HCl reacted, (b) the mass of [tex]MgCl_2[/tex] produced ([tex]Mg =24, Cl =35.5, H =1[/tex]).