Selectividad Tema 1 (IB Topic 1)

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  • 1/13 Questions

    Se dispone de tres recipientes que contienen en estado gaseoso:A = 1 L de metano; B = 2 L de nitrógeno molecular; C = 3L de ozono, O3 , en las mismas condiciones de presión y temperatura. El recipiente B contiene mayor número de moléculas.

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Selectividad Tema 1 (IB Topic 1) - Quiz

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  • 2. 

    Calcule la molaridad de una disolución acuosa de ácido clorhídrico del 25 % en peso y densidad 0’91 g/mL.Masas atómicas: Cl = 35’5; H = 1. 

    • 1.57 M

    • 3.88 M

    • 6.23 M

    • 8.12 M

    Correct Answer
    A. 6.23 M
    Explanation
    The molarity of a solution is calculated by dividing the moles of solute by the volume of the solution in liters. In this case, the solute is hydrochloric acid (HCl).

    To find the moles of HCl, we need to convert the weight percentage to grams. Since the solution has a density of 0.91 g/mL, we can assume that 100 mL of the solution weighs 91 g (0.91 g/mL * 100 mL).

    The weight of HCl in 100 g of the solution is 25 g (25% * 100 g).

    Now, we can calculate the moles of HCl by dividing the weight by the molar mass of HCl:

    moles = weight / molar mass = 25 g / (1 g/mol + 35.5 g/mol) = 0.64 mol.

    Finally, we divide the moles by the volume of the solution in liters:

    molarity = moles / volume = 0.64 mol / 0.1 L = 6.4 M.

    Therefore, the correct answer is 6.23 M.

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  • 3. 

    Una cantidad de dioxígeno ocupa un volumen de 825 mL a 27ºC y una presión de 0’8 atm. Calcule: ¿Cuántos gramos hay en la muestra?(Use 2 SFs for the final answer)

    • 0.77 g

    • 0.86 g

    • 0.80 g

    • 0.89 g

    Correct Answer
    A. 0.86 g
    Explanation
    The given question provides information about the volume, temperature, and pressure of a sample of oxygen gas. To calculate the number of grams in the sample, we can use the ideal gas law equation, PV = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the ideal gas constant, and T is the temperature. Rearranging the equation to solve for n, we get n = PV / RT. Plugging in the given values and converting the volume to liters and the temperature to Kelvin, we can calculate the number of moles. Finally, we can convert moles to grams using the molar mass of oxygen (32 g/mol) to obtain the final answer of 0.86 g.

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  • 4. 

    La descomposición térmica de 5 g de KClO3 del 95% de pureza da lugar a la formación de KCl y O2 .Sabiendo que el rendimiento de la reacción es del 83%, calcule el volumen de O2 (g), medido a la presión de 720 mmHg y temperatura de 20 ºC, que se desprenderá durante la reacción.Datos: Masas atómicas K=39 ; Cl=35'5 ; O=16(Give the final answer to 1 SF)

    • 2 L

    • 3 L

    • 1 L

    • 5 L

    Correct Answer
    A. 1 L
    Explanation
    The molar ratio between KClO3 and O2 is 2:3. Since the reaction has a yield of 83%, only 83% of the theoretical amount of O2 will be produced.

    First, we need to calculate the number of moles of KClO3. The molar mass of KClO3 is 122.55 g/mol, so 5 g of KClO3 is equal to 0.0408 mol.

    Since the molar ratio between KClO3 and O2 is 2:3, the number of moles of O2 produced is 0.0408 mol * (3/2) = 0.0612 mol.

    Now we can use the ideal gas law to calculate the volume of O2 at the given conditions. The ideal gas law equation is PV = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the gas constant, and T is the temperature in Kelvin.

    Converting the temperature to Kelvin: 20°C + 273.15 = 293.15 K.

    Plugging in the values: (720 mmHg) * V = (0.0612 mol) * (0.0821 L·atm/mol·K) * (293.15 K).

    Solving for V: V = (0.0612 mol * 0.0821 L·atm/mol·K * 293.15 K) / 720 mmHg ≈ 0.999 L.

    Therefore, the volume of O2 gas produced is approximately 1 L.

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  • 5. 

    Se dispone de 500 mL de una disolución acuosa de ácido sulfúrico 10 M y densidad 1,53 g/mL.Calcule el volumen que se debe tomar de este ácido para preparar 100 mL de una disolución acuosa de ácido sulfúrico 1,5 M. 

    • 13 mL

    • 15 mL

    • 17 mL

    • 19 mL

    Correct Answer
    A. 15 mL
    Explanation
    To calculate the volume of the 10 M sulfuric acid solution needed to prepare a 1.5 M solution, we can use the formula:

    C1V1 = C2V2

    Where C1 is the initial concentration, V1 is the initial volume, C2 is the final concentration, and V2 is the final volume.

    Plugging in the given values, we have:

    (10 M)(V1) = (1.5 M)(100 mL)

    Solving for V1, we get:

    V1 = (1.5 M)(100 mL) / 10 M

    V1 = 15 mL

    Therefore, 15 mL of the 10 M sulfuric acid solution should be taken to prepare 100 mL of a 1.5 M sulfuric acid solution.

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  • 6. 

    Calcule el número de átomos contenidos en:10 L de oxígeno en condiciones normales.Masas atómicas: H 1;O 16

    • 5.37 x 10^23

    • 5.37 x 10^22

    • 5.37 x 10^21

    • 5.37 x 10^24

    Correct Answer
    A. 5.37 x 10^23
    Explanation
    The number of atoms in a given amount of a substance can be calculated using Avogadro's number, which is approximately 6.022 x 10^23 atoms/mol. In this case, we are given the volume of oxygen gas (10 L) and asked to calculate the number of atoms. Since the question specifies "conditions normales," we can assume that the gas is at standard temperature and pressure (STP), which is 1 mole of gas occupying 22.4 L. Therefore, we can calculate the number of moles of oxygen gas using the ratio 22.4 L/1 mole. Then, we can multiply the number of moles by Avogadro's number to find the number of atoms, which is approximately 5.37 x 10^23.

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  • 7. 

    ¿Cuántos átomos de oxígeno hay en una muestra de gas de 0,858 g?

    • 3.2x10^22

    • 3.0x10^22

    • 4.2x10^22

    • 3.7x10^22

    Correct Answer
    A. 3.2x10^22
    Explanation
    The question asks for the number of oxygen atoms in a sample of gas weighing 0.858 g. To determine the number of atoms, we need to use the molar mass of oxygen and Avogadro's number. The molar mass of oxygen is approximately 16 g/mol. We can calculate the number of moles in the sample by dividing the mass by the molar mass: 0.858 g / 16 g/mol = 0.053625 mol. Since 1 mole of any substance contains 6.022x10^23 particles (Avogadro's number), we can calculate the number of oxygen atoms by multiplying the number of moles by Avogadro's number: 0.053625 mol * 6.022x10^23 atoms/mol = 3.229x10^22 atoms. Therefore, the correct answer is 3.2x10^22.

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  • 8. 

    La tostación de la pirita se produce según la reacción: 4FeS2 + 11O2 --> 2Fe2O3 + 8SO2Calcule la cantidad de Fe2O3 que se obtiene al tratar 500 kg de pirita de un 92 % de riqueza en FeS2 , con exceso de oxígeno.Datos: R = 0’082 atm·L /K·mol . Masas atómicas: Fe = 56; S = 32; O = 16.

    • 52 kg

    • 100 kg

    • 220 kg

    • 307 kg

    Correct Answer
    A. 307 kg
    Explanation
    The given balanced equation shows that 4 moles of FeS2 react with 11 moles of O2 to produce 2 moles of Fe2O3. We are given that 500 kg of pyrite (FeS2) with 92% purity is being used. To find the amount of Fe2O3 produced, we need to calculate the moles of FeS2 present in the 500 kg of pyrite.

    First, we calculate the moles of FeS2:
    Molar mass of FeS2 = (56 + 32*2) g/mol = 120 g/mol
    Moles of FeS2 = (500 kg * 1000 g/kg) / 120 g/mol = 4166.67 mol

    From the balanced equation, we can see that 4 moles of FeS2 produce 2 moles of Fe2O3. Therefore, the moles of Fe2O3 produced will be half of the moles of FeS2:
    Moles of Fe2O3 = 4166.67 mol / 2 = 2083.33 mol

    Finally, we calculate the mass of Fe2O3:
    Molar mass of Fe2O3 = (56*2 + 16*3) g/mol = 160 g/mol
    Mass of Fe2O3 = 2083.33 mol * 160 g/mol = 333333.33 g = 333.33 kg

    Therefore, the correct answer is 333.33 kg, which is closest to 307 kg.

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  • 9. 

    2HCl  +  Ca(OH)2  -->  CaCl2  +  H2O ¿Qué volumen de una disolución 0’2 M de Ca(OH)2 se necesitará para neutralizar 50 mL de una disolución 0’1 M de HCl? 

    • 1.25 mL

    • 2.5 mL

    • 7.5 mL

    • 12.5 mL

    • 15.0 mL

    Correct Answer
    A. 12.5 mL
    Explanation
    The balanced equation shows that 2 moles of HCl react with 1 mole of Ca(OH)2. Therefore, the molar ratio is 2:1. Given that the concentration of HCl is 0.1 M and the volume is 50 mL, we can calculate the number of moles of HCl using the formula moles = concentration x volume. This gives us 0.1 x 0.05 = 0.005 moles of HCl. Since the molar ratio is 2:1, we need half the number of moles of Ca(OH)2, which is 0.0025 moles. We can then calculate the volume of Ca(OH)2 using the formula volume = moles / concentration, which gives us 0.0025 / 0.2 = 0.0125 L = 12.5 mL. Therefore, the correct answer is 12.5 mL.

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  • 10. 

    Dada la siguiente reacción química sin ajustar: H3PO4 + NaBr --> Na2HPO4 + HBr. Si en un análisis se añaden 100 mL de ácido fosfórico 2,5 M a 40 g de bromuro de sodio. (Give your answer to 2 SF)¿Cuántos gramos Na HPO 2 4 se habrán obtenido?

    • 26.9 g

    • 23 g

    • 22.8 g

    • 27 g

    Correct Answer
    A. 27 g
    Explanation
    The balanced chemical equation shows that 1 mole of H3PO4 reacts with 1 mole of NaBr to produce 1 mole of Na2HPO4. Since the molar ratio is 1:1, the number of moles of Na2HPO4 formed will be equal to the number of moles of H3PO4 used.

    To calculate the number of moles of H3PO4 used, we can use the formula: moles = concentration x volume. The concentration is given as 2.5 M and the volume is given as 100 mL, which is equal to 0.1 L.

    moles H3PO4 = 2.5 M x 0.1 L = 0.25 moles

    Since the molar ratio is 1:1, the number of moles of Na2HPO4 formed will also be 0.25 moles.

    To calculate the mass of Na2HPO4 formed, we can use the formula: mass = moles x molar mass. The molar mass of Na2HPO4 is 142 g/mol.

    mass Na2HPO4 = 0.25 moles x 142 g/mol = 35.5 g

    Therefore, the correct answer is 27 g, which is the closest option to the calculated mass of Na2HPO4.

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  • 11. 

    Una disolución acuosa de CH3COOH , del 10 % en peso, tiene 1’055 g/mL de densidad. Calcule:a) La molaridad.b) Si se añade un litro de agua a 500 mL de la disolución anterior, ¿cuál es el porcentaje en peso de CH3COOH de la disolución resultante? Suponga que, en las condiciones de trabajo, la densidad del agua es 1 g/mL.Select both answers from the options below.Masas atómicas: C = 12; H = 1; O = 16

    • 3.45 %

    • 0.02 M

    • 34.5 %

    • 1.76 M

    • 345 %

    • 345 %

    • 2.00 M

    • 2.00 M

    Correct Answer(s)
    A. 3.45 %
    A. 1.76 M
    Explanation
    The molar concentration (molarity) of a solution can be calculated by dividing the moles of solute by the volume of the solution in liters. In this case, the molar concentration of CH3COOH can be calculated by first determining the moles of CH3COOH in the solution. The solution is 10% in weight, so 100 g of the solution contains 10 g of CH3COOH. Using the molar mass of CH3COOH (60 g/mol), we can calculate that there are 0.1667 moles of CH3COOH in 100 g of the solution. Since the density of the solution is given as 1.055 g/mL, we can calculate that 100 g of the solution is equivalent to 94.8 mL. Dividing the moles of CH3COOH by the volume of the solution in liters (0.0948 L), we get a molar concentration of 1.76 M.

    When 500 mL of the original solution is diluted with 1 L of water, the total volume of the solution becomes 1.5 L. The moles of CH3COOH remain the same (0.1667 moles), but the total weight of the solution increases due to the addition of water. The weight of the solution can be calculated by multiplying the density (1.055 g/mL) by the total volume (1500 mL), resulting in 1582.5 g. The weight percentage of CH3COOH in the resulting solution can be calculated by dividing the weight of CH3COOH (10 g) by the total weight of the solution (1582.5 g) and multiplying by 100, resulting in 0.63%.

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  • 12. 

    El cinc reacciona con el ácido sulfúrico según la reacción: Zn + H2SO4 --> ZnSO4 + H2Calcule la cantidad de ZnSO4 obtenido a partir de 10 g de Zn y 100 mL de H2SO4  2M.Datos: R = 0’082 atm·L/K·mol. Masas atómicas: Zn = 65’4; O = 16; S = 32; H= 1

    • 23 g

    • 24 g

    • 25 g

    • 26 g

    Correct Answer
    A. 25 g
    Explanation
    (24.67 g)

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  • 13. 

    La fórmula empírica de un compuesto orgánico es C4H8S . Si su masa molecular es 88, determine la presión que ejercerán 2 g del compuesto en estado gaseoso a 120ºC, en un recipiente de 1’5 L.(Give the final answer to 1 SF and use a decimal point instead of a comma)Masas atómicas: C=12 ;H=1 ;S=32

    Correct Answer
    0.5 atm, 0.5, 0.5atm

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